PrEP
PrEP is a highly effective medication that helps prevent HIV before exposure. This FAQ covers how it works, who should take it, how to access it, dosing options, safety, and its role in HIV prevention
Understanding PrEP
What is PrEP and how does it help prevent HIV?
PrEP (Pre-Exposure Prophylaxis) is a medication that helps prevent HIV before exposure to the virus. It’s taken by people who are at risk of getting HIV, such as those with HIV-positive partners, individuals who have multiple sexual partners, or people who inject drugs. PrEP works by using antiretroviral drugs that stop HIV from multiplying in the body, preventing infection if someone is exposed to the virus.
How well does PrEP work at preventing HIV?
PrEP is highly effective when taken as prescribed:
Daily PrEP reduces the risk of getting HIV from sex by 99% and from injection drug use by at least 74%.
On-demand PrEP (taking pills around the time of sex) has been shown to be about 86-97% effective for men who have sex with men.
Effectiveness drops if PrEP is not taken consistently, so it’s important to follow the recommended schedule.
How is PrEP different from PEP (Post-Exposure Prophylaxis)?
PrEP and PEP are both used to prevent HIV but in different situations:
PrEP is taken before exposure to HIV, on an ongoing basis, by people who are at continued risk.
PEP (Post-Exposure Prophylaxis) is taken after a possible HIV exposure (e.g., unprotected sex, sharing needles) and must be started within 72 hours of exposure. PEP is taken for 28 days and is an emergency treatment, while PrEP is for regular prevention
Who should consider taking PrEP?
PrEP is recommended for anyone at high risk of HIV, including:
People with an HIV-positive partner (especially if their partner is not on treatment).
Gay, bisexual, and other men who have sex with men, particularly those who don’t always use condoms.
People who have multiple sexual partners or partners whose HIV status is unknown.
Sex workers who may have clients with unknown HIV status.
People who inject drugs and share needles.
People who have recently used PEP multiple times.
If you think you might be at risk, a TeleTest physician can help determine if PrEP is right for you.
How does PrEP fit into a complete HIV prevention plan?
PrEP is one part of a broader strategy to prevent HIV. It works best when combined with other prevention methods such as:
Using condoms to reduce the risk of HIV and other sexually transmitted infections (STIs).
Getting regular HIV and STI testing to stay informed about your health.
Encouraging HIV-positive partners to stay on treatment, which lowers their viral load and reduces transmission risk.
Using clean needles if you inject drugs. No single method is 100% effective, but combining strategies provides the best protection.
Can I still use condoms while taking PrEP?
Yes! Using condoms along with PrEP provides the best protection. While PrEP significantly reduces the risk of HIV, condoms also:
Prevent other sexually transmitted infections (STIs) like chlamydia, gonorrhea, and syphilis.
Offer extra protection if you miss a PrEP dose. If you’re comfortable using condoms, they are still a great way to protect your overall sexual health.
Are there different ways to take PrEP (daily vs. as needed)?
Yes, there are two main ways to take PrEP:
Daily PrEP: One pill every day, which provides continuous protection and is recommended for all people at risk.
On-Demand (Event-Based) PrEP: This method is used by some men who have sex with men. It involves taking:
Two pills 2-24 hours before sex.
One pill every day you are having sex.
One last pill 48 hours after your last sexual encounter. This method is not recommended for women or people who inject drugs because it may not provide full protection.
Why is On-Demand (Event-Based) PrEP less effective in women and people who inject drugs?
PrEP is less effective for women and people who inject drugs when not taken daily because the drug levels in vaginal and blood tissues take longer to build up compared to rectal tissue.
For women: The active drugs in PrEP (tenofovir and emtricitabine) do not reach high enough concentrations in vaginal tissue as quickly as they do in rectal tissue. Studies show that daily use is needed to maintain protection, while taking PrEP only around the time of sex (on-demand PrEP) does not provide reliable protection.
For people who inject drugs: Since HIV transmission occurs through the bloodstream, consistent drug levels in the blood are needed for protection. Daily PrEP ensures that drug levels stay high enough to block the virus if exposure occurs.
For these reasons, on-demand PrEP is not recommended for women or injection drug users—they should take PrEP every day for the best protection.
Eligibility
Who qualifies for PrEP?
PrEP is for people at higher risk of HIV. You may qualify if you:
Have a sexual partner with HIV (especially if they are not on treatment).
Have multiple sexual partners or don’t always use condoms.
Are a man who has sex with men.
Are a transgender person at risk of HIV.
Inject drugs and share needles.
Have had a recent sexually transmitted infection (STI).
A healthcare provider can assess your risk and determine if PrEP is right for you.
What are the risk factors that indicate someone may benefit from PrEP?
You may benefit from PrEP if you:
Have condomless anal or vaginal sex with partners of unknown HIV status.
Have a recent STI, which can increase the risk of HIV.
Have multiple sexual partners or a partner who has multiple partners.
Have used PEP (Post-Exposure Prophylaxis) multiple times.
Share needles or drug equipment with others.
Have a partner living with HIV who is not consistently on treatment. If any of these apply to you, PrEP could be a good option.
Is PrEP recommended for heterosexual individuals?
Yes! While HIV rates are lower among heterosexual people, PrEP is recommended for:
Heterosexual individuals with an HIV-positive partner who is not on treatment.
People who have condomless vaginal or anal sex with multiple partners.
People whose partners are at higher risk of HIV (e.g., men who have sex with men, people who inject drugs). Women should take daily PrEP rather than on-demand dosing for full protection.
Can people who inject drugs (PWID) use PrEP?
Yes, PrEP is an option for people who inject drugs, but daily use is required for it to work effectively. PrEP is recommended for PWID who:
Share needles, syringes, or drug equipment with others.
Have a partner who injects drugs and may have HIV.
Engage in both drug use and sex work, which may increase risk. Even with PrEP, harm reduction strategies like using sterile needles and not sharing equipment are important.
Is PrEP appropriate for transgender individuals?
Yes, PrEP is safe and effective for transgender men and women who are at risk of HIV.
Transgender women benefit from daily PrEP, but studies suggest that on-demand PrEP is not recommended due to concerns about lower drug levels in vaginal tissue.
Transgender men who have receptive vaginal sex should also take daily PrEP. PrEP does not interfere with hormone therapy, and both can be safely used together.
Can couples where one partner has HIV use PrEP?
Yes! If one partner has HIV and the other does not, PrEP can provide extra protection. This is sometimes called a “mixed-status” or HIV-discordant couple.
If the HIV-positive partner is on effective treatment and has an undetectable viral load, the risk of transmission is extremely low (Undetectable = Untransmittable or U=U).
However, PrEP is still an option for added peace of mind, especially if the HIV-positive partner’s viral load is not consistently undetectable.
How do I know if I should take PrEP or just use PEP after a high-risk exposure?
Use PEP if: You had a one-time high-risk exposure (e.g., condom broke, shared a needle, or had unprotected sex with a partner of unknown HIV status). PEP must be started within 72 hours and taken for 28 days.
Use PrEP if: You have ongoing risk of HIV (e.g., multiple partners, inconsistent condom use, an HIV-positive partner). PrEP is taken before exposure and is used for continuous protection. If you’ve needed PEP more than once, you should consider switching to PrEP.
What are the eligibility criteria for publicly funded PrEP in Canada?
PrEP is publicly funded in many provinces for people at high risk of HIV. The criteria generally include:
Men who have sex with men (MSM) or transgender individuals with multiple partners or recent STIs.
Heterosexual individuals with an HIV-positive partner who is not on treatment.
People who inject drugs and share equipment.
People who have had multiple courses of PEP.
Other risk factors depending on the province you're in.
Getting PrEP
How do I get PrEP?
To get PrEP, you need to:
See a doctor or nurse practitioner for an assessment.
Get tested for HIV and other conditions to ensure it’s safe to start PrEP.
Get a prescription if you qualify.
Pick up PrEP at a pharmacy (it may be covered by insurance or public health programs).
Do I need a prescription for PrEP?
Yes, PrEP requires a prescription from a healthcare provider. You can’t buy it over the counter. A doctor or nurse practitioner will assess your risk, do necessary tests, and provide a prescription if appropriate.
Where can I go to talk to a doctor about PrEP?
You can discuss PrEP with:
Any TeleTest physician
Your family doctor (if they are familiar with PrEP).
Sexual health clinics (these often have PrEP specialists).
HIV clinics or infectious disease specialists.
What tests do I need before I start taking PrEP?
Before starting PrEP, you’ll need:
An HIV test (PrEP is only for HIV-negative individuals).
Kidney function tests (PrEP can affect kidney health).
Hepatitis B and C tests (PrEP can also treat hepatitis B, so this must be monitored).
Sexually transmitted infection (STI) screening.
Pregnancy test (if applicable).
These tests are important to ensure PrEP is safe for you and to monitor any potential health concerns.
How often do I need to see a doctor while on PrEP?
After starting PrEP, you should see a doctor:
After 1 month for follow-up blood work.
Every 3 months for ongoing HIV and STI testing, kidney monitoring, and prescription renewals.
Anytime you experience side effects or concerns.
These visits ensure that PrEP is still right for you and that you’re staying healthy.
What if I can’t afford PrEP? Are there assistance programs?
Yes! If PrEP is not fully covered in your province, you can explore:
Provincial health plans (check if you qualify for government-funded coverage).
Private insurance (many plans include PrEP, so ask your provider).
Manufacturer assistance programs (some drug companies offer financial aid).
Community-based HIV organizations (they may help you access lower-cost PrEP).
How do I switch from using PEP to taking PrEP regularly?
If you’ve used PEP (Post-Exposure Prophylaxis) multiple times, you might want to switch to PrEP for ongoing protection. The process is:
Complete your full 28-day course of PEP.
Get an HIV test to confirm you remain HIV-negative.
If still at risk, start PrEP immediately after finishing PEP (your doctor can provide a prescription in advance). Switching from PEP to PrEP ensures continuous protection without a gap in coverage.
How to Take PrEP
How often do I need to take PrEP?
Daily PrEP: Take one pill every day for continuous protection. This is the most reliable way to prevent HIV.
On-Demand PrEP (for some men who have sex with men): Take pills only around the time of sex. This method is not recommended for women or people who inject drugs. Our doctors can help decide which method is best for you
Injectable PrEP: Given as a shot every two months for continuous protection. This is a good option for people who have trouble taking pills daily.
What happens if I miss a dose?
Truvada (daily PrEP pills)
If you miss a dose within 12 hours of your usual time: Take the missed dose with food as soon as possible, then continue with your regular schedule.
If you miss a dose by more than 12 hours and it’s close to your next dose: Skip the missed dose and take your next scheduled dose at the usual time.
Do not take more than one dose per day or double up to make up for a missed dose.
Descovy (daily PrEP pills)
If you miss a dose within 18 hours of your usual time: Take the missed dose with or without food as soon as possible, then continue with your regular schedule.
If you miss a dose by more than 18 hours: Skip the missed dose and take your next scheduled dose at the usual time.
Do not take more than one dose per day or double up to make up for a missed dose.
If you frequently miss doses, talk to your doctor about ways to stay on track or whether a different PrEP method may work better for you.
How long does it take for daily PrEP to provide full protection?
The time it takes for daily PrEP (oral pills) to become fully effective depends on the type of exposure:
For anal sex (men who have sex with men - MSM): PrEP reaches full effectiveness after about 7 days of daily use.
For vaginal sex and injection drug use: PrEP reaches full effectiveness after about 21 days of daily use.
The difference is due to how the medication concentrates in different body tissues. PrEP builds up faster in rectal tissue, which is why it provides protection for anal sex within a week, whereas it takes longer to reach effective levels in vaginal and blood tissues.
Until PrEP reaches full effectiveness, it is recommended to use additional prevention methods such as condoms.
How does on-demand PrEP (2-1-1) work, and when does it provide protection?
On-demand PrEP (also called 2-1-1 dosing) is an alternative to daily PrEP for men who have sex with men (MSM) engaging in receptive anal sex. This method is not recommended for vaginal sex or injection drug use.
The dosing schedule is:
Before sex: Take 2 PrEP pills between 2 and 24 hours before sex.
Taking the pills closer to 24 hours before sex is better to ensure optimal protection.
After sex: Take 1 pill 24 hours after the first dose, then 1 more pill 24 hours later (48 hours after the first dose).
Protection begins as early as 2 hours after the first two-pill dose, but levels are strongest after 24 hours. Full protection is only achieved if the entire 2-1-1 regimen is completed. Skipping the post-sex doses may lower protection.
Studies have shown that properly using on-demand PrEP can reduce HIV risk by about 86%.
Is on-demand PrEP effective for vaginal sex or injection drug use?
No, on-demand PrEP is not recommended for vaginal sex or for people who inject drugs. Research has shown that PrEP drugs take longer to concentrate in vaginal and blood tissues, meaning on-demand dosing may not provide sufficient protection for these types of HIV exposure.
For vaginal sex and injection drug use, daily PrEP is the recommended method, with full protection reached after about 21 days of daily use.
How quickly does injectable PrEP (cabotegravir) start working?
Injectable PrEP (cabotegravir, brand name Apretude) starts providing protection within a few days after the first injection. Some studies suggest that protective drug levels are reached in about 7 days, but there is no officially recommended “lead-in” period like the 21-day guideline for oral PrEP.
To ensure continuous protection, it is important to follow the prescribed injection schedule:
First injection (Month 0) – Provides initial protection.
Second injection (Month 1) – Boosts drug levels for ongoing protection.
Subsequent injections every 2 months – Required to maintain effectiveness.
While cabotegravir builds up quickly, some health authorities suggest using additional protection methods, such as condoms, until the second injection at one month. This ensures optimal drug levels for maximum protection against HIV.
Because there is no published data on the time to effectiveness and the drug was approved without specifying his 'lead in time', we recommend waiting until 7 days after the 2nd dose is administered.
Bottom line: Although injectable PrEP works relatively fast, patients should stay cautious during the first month and use extra precautions if needed until the second injection is received.
Can I stop PrEP and restart later if my risk level changes?
Yes! You can safely stop PrEP if you are no longer at risk, but you should:
Continue PrEP for at least 28 days after your last exposure to ensure protection.
Get an HIV test before restarting PrEP.
If restarting, follow the waiting period: 7 days for anal sex, 21 days for vaginal sex or injection drug use.
Injectable PrEP may require temporary oral PrEP if there’s a delay in getting your next shot
On Demand PrEP - Event Based Dosing
What is On-Demand PrEP?
On-Demand PrEP, also known as event-based dosing (EBD) or 2-1-1 PrEP, is an alternative to daily PrEP for men who have sex with men (MSM) who want protection only around the time of sexual activity. Instead of taking a pill every day, On-Demand PrEP follows this schedule:
Take 2 pills of TDF/FTC (Truvada or generic equivalent) 2–24 hours before sex.
Take 1 pill per day if you continue having sex.
Take the final pill 48 hours after the last sexual encounter.
This method provides similar (though lower) protection to daily PrEP for MSM when taken correctly. However, it is not recommended for everyone.
Which PrEP Brands Are Available for On-Demand Use?
Currently, only TDF/FTC-based PrEP (Truvada or generics) is studied and recommended for On-Demand PrEP.
Truvada (brand name) – Contains tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC).
Generic TDF/FTC – Available in Canada at a lower cost.
Descovy (TAF/FTC) – NOT approved for On-Demand use because it has not been studied for this purpose.
Who is Eligible for On-Demand PrEP?
On-Demand PrEP is only recommended for men who have sex with men (MSM) who: ✔ Have infrequent sexual activity (less than twice a week). ✔ Can plan when they will have sex (so they can take the first dose on time). ✔ Do not have hepatitis B (TDF can suppress hepatitis B, and stopping suddenly can cause flare-ups).
Who Should NOT Use On-Demand PrEP? ❌ Cisgender women and transgender individuals engaging in vaginal sex (Drug levels take longer to build up in vaginal tissue, making On-Demand PrEP less reliable). ❌ People who inject drugs (Daily PrEP is recommended instead). ❌ Anyone who has frequent or unpredictable sex (Daily PrEP may be more suitable).
Does TeleTest Provide On-Demand PrEP Prescriptions?
No, TeleTest does not prescribe On-Demand (Event-Based) PrEP. At this time, we only provide prescriptions for daily PrEP, which is the most widely recommended and studied method for HIV prevention. If you are interested in On-Demand PrEP, we recommend speaking with a healthcare provider or a specialized sexual health clinic to discuss your options.
Stopping PrEP
Daily Oral PrEP (TDF/FTC)
How long should I continue PrEP after my last exposure if I take daily oral PrEP for receptive anal sex?
Continue daily PrEP for at least 2 days (48 hours) after your last potential HIV exposure via receptive anal sex.
Explanation: This short “tail” period is sufficient because drug concentrations remain high in rectal tissue for a couple of days, maintaining protection against HIV even after stopping PrEP.
How long should I continue PrEP after my last exposure if I take daily oral PrEP for vaginal sex or injection drug use?
Continue daily PrEP for at least 7 days after your last exposure via vaginal sex or injection drug use.
Explanation: Vaginal tissues and drug injection sites require a longer "tail period" due to slower drug absorption. Taking PrEP for a full 7 days after the last exposure ensures sufficient protective drug levels before stopping.
Long-Acting Injectable PrEP (Cabotegravir/Apretude)
How long does cabotegravir (Apretude) stay in my system after stopping injectable PrEP?
Cabotegravir is known to provide strong protection for about 2 months after your last injection. Although the drug remains detectable in your system for up to a year, its full protective effect is only guaranteed during those first 2 months. Because we don’t yet have guidance on how long maximum protection lasts beyond that point, we recommend using an additional HIV prevention method (such as daily oral PrEP or condoms) after 2 months.
Since oral PrEP also requires time to become fully effective, here are some examples of when you should begin it:
For men who have sex with men (MSM) engaging in anal sex: Start oral PrEP at least 7 days before your next cabotegravir injection would have been due.
For individuals engaging in vaginal sex or using injection drugs: Begin oral PrEP at least 21 days before your next scheduled cabotegravir injection.
This approach helps ensure you have continuous protection against HIV.
Injectable PrEP (Apretude)
What is Injectable PrEP?
Injectable PrEP is an HIV prevention option using long-acting cabotegravir (Apretude), given as a shot every two months instead of taking daily pills. It provides continuous protection against HIV for people at risk.
How is Injectable PrEP different from daily PrEP pills?
Injectable PrEP is given every two months, while daily PrEP requires a pill every day.
It is a good option for those who struggle with daily pill-taking.
Both options are highly effective when taken as prescribed
How often do I need to get the PrEP injection?
The first two shots are one month apart.
After that, injections are given every two months to maintain protection.
Is Injectable PrEP more effective than daily pills?
Studies show that injectable PrEP is at least as effective—if not more effective—than daily PrEP pills, especially for people who have trouble taking pills consistently.
What tests do I need before starting Injectable PrEP?
Before starting, you’ll need:
An HIV test to confirm you’re negative.
Kidney and liver function tests.
Hepatitis B and C screening.
STI screening
Can I switch from daily PrEP pills to Injectable PrEP?
Yes! If you're already on PrEP pills and want to switch, a TeleTest doctor may suggest:
Taking a lead-in period of oral cabotegravir pills for a few weeks to check for side effects.
Or, starting with the injection directly after an HIV test.
What happens if I miss an injection?
If you miss a scheduled injection, get it as soon as possible.
If too much time has passed, your doctor may recommend taking PrEP pills temporarily until you can restart the injections.
Truvada vs. Descovy for PrEP
How effective are Truvada and Descovy in preventing HIV?
Both Truvada (TDF/FTC) and Descovy (TAF/FTC) are highly effective in preventing HIV when taken as prescribed. Studies show that daily PrEP with either medication can reduce the risk of getting HIV from sex by about 99% with consistent use (thought he protection rate is lower with injection drug use).
In the DISCOVER trial, Descovy was found to be equally effective (non-inferior) to Truvada for men who have sex with men (MSM) and transgender women.
Adherence is key—PrEP works best when taken daily, as missed doses can lower protection.
What are the side effects of Truvada and Descovy? Do they affect bone or kidney health?
Both PrEP options are well tolerated, and most users do not experience serious side effects.
Short-term side effects:
Some people experience mild nausea, headache, or diarrhea when they first start PrEP.
These symptoms, often called “startup syndrome,” usually go away within a few weeks.
Long-term effects:
Bone health:
Truvada (TDF/FTC) may cause a small decrease in bone mineral density (~1%), but this loss reverses after stopping PrEP. In the context of age related bone mineral density losses, this 1% value is relatively small in the grand scheme of things.
Descovy (TAF/FTC) has less impact on bones and is preferred for individuals with osteoporosis or at risk of fractures.
Kidney health:
Truvada (TDF/FTC) can cause minor kidney function changes in some users, requiring regular kidney function monitoring.
Descovy (TAF/FTC) has less impact on kidney function, making it a safer choice for those with existing kidney conditions.
Weight & cholesterol:
Descovy users gained slightly more weight (~1-2 kg per year) compared to Truvada users.
Truvada slightly lowers cholesterol, while Descovy may slightly raise cholesterol levels.
Bottom line: Truvada and Descovy have similar short-term side effects, but Descovy is easier on bones and kidneys, while Truvada is more widely available and has a longer safety record.
Is it safe to take Truvada or Descovy if I have other health conditions like kidney disease or osteoporosis?
Yes, but your doctor may recommend one over the other based on your health history:
Kidney disease: Descovy is preferred because it has less impact on kidney function than Truvada.
Osteoporosis or low bone density: Descovy is safer since Truvada may cause a small decrease in bone density.
Hepatitis B (HBV) infection: Both Truvada and Descovy also treat hepatitis B, so if you have HBV, stopping PrEP suddenly may cause a flare-up of the virus—talk to your doctor first.
Can I use Truvada or Descovy as PrEP for many years?
Yes! PrEP is meant for long-term use as long as you are at risk for HIV.
Long-term safety studies show no major health concerns for people using PrEP for years.
Your doctor will monitor your kidney function (for Truvada users) and bone health (if needed) every few months.
If your risk changes, you can stop and restart PrEP safely with medical guidance.
Most people can stay on PrEP for as long as they need it, with regular check-ups to ensure safety.
Do Truvada or Descovy interact with other medications?
Both PrEP options have very few drug interactions, but be sure to inform your doctor if you take:
HIV or hepatitis B medications (to avoid drug resistance).
Tuberculosis (TB) antibiotics (rifampin may lower Descovy effectiveness).
Certain seizure medications (phenytoin, carbamazepine may affect drug levels).
NSAIDs (like ibuprofen/naproxen)—frequent use with Truvada may require extra kidney monitoring.
Most common medications, including birth control and hormone therapy, do NOT interfere with PrEP.
How much do Truvada and Descovy cost? Is generic Truvada available?
Truvada (TDF/FTC) is available as a generic, making it much cheaper than Descovy.
Descovy is still under patent and costs significantly more unless covered by insurance.
Canada: Generic Truvada costs ~$250/month; Descovy costs $1,000–$1,200/month. Many provincial health plans and private insurance plans cover PrEP.
Who should take Truvada, and who should take Descovy?
Effectiveness
99%+ protection
99%+ protection
Kidney safety
May slightly reduce kidney function
Safer for kidneys
Bone health
May cause slight bone loss (~1%)
No significant bone loss
Weight & cholesterol
May slightly lower cholesterol
May cause slight weight gain & increase cholesterol
Populations approved for
ll people, including MSM, women, and people who inject drugs (PWID)
Only approved for MSM and transgender women (not studied in cisgender women or PWID)
Availability & cost
Generic available, much cheaper
Brand-only, more expensive
Best for:
Truvada – Most people, especially those needing a lower-cost option.
Descovy – Those with kidney issues, osteoporosis, or who have insurance coverage for it.
Important note: Descovy is NOT approved for cisgender women or people who inject drugs, as it was not studied in these populations.
PrEP and Bone Health
How does PrEP affect my bone density?
PrEP containing tenofovir disoproxil fumarate (TDF/FTC) (e.g., Truvada) has been linked to a small drop in bone mineral density (BMD)—about 1–2% loss in the spine and hip during the first 6–12 months. This occurs because tenofovir can affect calcium and phosphate levels in bones. However, studies show that this loss does not lead to an increased risk of fractures and is considered clinically minor when weighed against PrEP’s ability to prevent HIV.
Is bone density loss from PrEP reversible?
Yes! Bone density loss from TDF/FTC PrEP is reversible once you stop taking it. Studies show that BMD returns to pre-PrEP levels within 6–12 months after stopping. Even older adults and adolescents who experienced bone loss on PrEP regained bone mass after discontinuing.
Should I take calcium or vitamin D while on PrEP?
Maintaining adequate calcium and vitamin D is important for overall bone health, whether or not you take PrEP. While supplements are not required for all PrEP users, they can help reduce bone loss and improve density, especially for those with low vitamin D levels. Foods rich in calcium (dairy, leafy greens, fortified foods) and vitamin D (fatty fish, eggs, sunlight exposure) can support strong bones. We recommend everyone supplement with 2000IU of Vitamin D daily.
Am I at greater risk for fractures if I take PrEP?
No. Large clinical trials show that PrEP does not increase fracture risk. A study combining data from 13 PrEP trials found no difference in fractures between those taking PrEP and those taking a placebo. Even though a small drop in bone density occurs with TDF/FTC, fractures are not more common in PrEP users.
How does bone loss from PrEP compare to age-related bone loss?
Bone loss from aging is a gradual and permanent process, while PrEP-related bone loss is temporary and reversible.
PrEP-related loss: ~1–2% decrease in BMD, which recovers after stopping PrEP.
Aging-related loss: ~0.5–2% per year starting in middle-age, which continues without treatment and can lead to osteoporosis.
Postmenopausal women and older adults naturally lose 10–20% of their bone mass over a few decades, compared to a small temporary drop on PrEP.
Are there PrEP options that do not cause bone loss?
Yes! Tenofovir alafenamide (TAF/FTC, brand name Descovy) is a newer PrEP option that has little to no impact on bone density.
In clinical trials, people taking TAF/FTC actually gained bone density, while those on TDF/FTC had slight declines.
Health agencies in Canada have studied the per-act risk of HIV transmission (the probability of infection from a single exposure if the source is HIV-positive and no preventive measures are used). The estimated risks are:
Injectable PrEP (Apretude) does not contain tenofovir and does not affect bone health.
If you have osteoporosis or are at higher risk of bone loss, talk to your doctor about switching to a bone-friendly PrEP option like TAF/FTC or injectable PrEP.
HIV Transmission
What is the risk of getting HIV from a single exposure?
Health agencies in Canada have studied the per-act risk of HIV transmission (the probability of infection from a single exposure if the source is HIV-positive and no preventive measures are used). The estimated risks are:
Receptive anal intercourse (bottom)
~1.4% (≈1 in 70 chance)
Insertive anal intercourse (top)
~0.11% (≈1 in 900 chance)
Receptive vaginal intercourse (female)
~0.08% (≈1 in 1,250 chance)
Insertive vaginal intercourse (male)
~0.04% (≈1 in 2,500 chance)
Oral sex (giving or receiving)
<0.04% (very low per act)
Sharing injection needles (IDU)
~0.6% (≈1 in 160 chance per use)
Needlestick injury (e.g., healthcare worker exposure)
~0.23% (≈1 in 435 chance)
Blood transfusion (from an HIV+ donor)
~92.5% (≈1 in 1.1 chance)
Note: These are mid-range estimates, and actual risk may vary based on viral load, presence of STIs, and other factors.
Reference data: Patel, P., Borkowf, C. B., Brooks, J. T., Lasry, A., Lansky, A., & Mermin, J. (2014). Estimating per-act HIV transmission risk: A systematic review. AIDS, 28(10), 1509–1519. https://doi.org/10.1097/QAD.0000000000000298
Does the risk of HIV vary between different types of sex?
Yes. Receptive anal sex (bottoming) carries the highest sexual transmission risk (~1.4%) because the rectal lining is thin and absorbs the virus more easily. Insertive anal sex (topping) has a lower risk (~0.11%) but is still higher than vaginal intercourse. Vaginal sex has lower, but still significant, risks (~0.08% for receptive, ~0.04% for insertive).
Is HIV transmission possible from oral sex?
HIV transmission through oral sex is extremely rare. The risk per act is estimated at less than 0.04%, meaning it is considered “low but not zero.” Transmission is more likely if there are cuts, sores, bleeding gums, or an untreated STI in the mouth or genitals.
What is the risk of getting HIV from sharing needles?
Sharing injection needles has a higher risk (~0.6% per use) because the virus enters directly into the bloodstream. Using sterile needles and harm reduction services can greatly reduce this risk.
How does HIV transmission from needlestick injuries compare?
Healthcare workers who experience needlestick injuries from HIV-positive patients have a ~0.23% risk (about 1 in 435 chance) of infection per incident. Post-Exposure Prophylaxis (PEP) can reduce this risk significantly if started within 72 hours.
What factors increase or decrease the risk of HIV transmission?
Several factors can increase transmission risk, including:
High viral load in the HIV-positive partner (if untreated).
The presence of STIs, which can cause inflammation and make transmission easier.
Cuts, tears, or mucosal damage in the genital or anal area.
Factors that reduce transmission risk include:
PrEP (Pre-Exposure Prophylaxis) – reduces sexual HIV risk by 99% if taken consistently.
PEP (Post-Exposure Prophylaxis) – can prevent HIV if taken within 72 hours after exposure.
Condom use – significantly reduces risk for all types of sexual exposure.
Undetectable = Untransmittable (U=U) – People with HIV on treatment with an undetectable viral load cannot transmit HIV sexually.
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