Guide to HIV PrEP and DoxyPEP in Singapore

Two preventive tools now sit alongside condoms and regular testing in Singapore sexual health care. HIV pre-exposure prophylaxis (PrEP) is an antiretroviral taken before exposure to stop HIV establishing itself. Doxycycline post-exposure prophylaxis (DoxyPEP) is a single antibiotic dose taken after condomless sex to reduce the chance of some bacterial infections taking hold.

They are often discussed together because many people who benefit from one are considering the other. They work on different organisms, follow different schedules, and carry different trade-offs. This guide uses full generic drug names throughout, which the service pages avoid, so that you can follow the regimens precisely. Brand names are deliberately not used.

If you would rather go straight to the services, see HIV PrEP and DoxyPEP.

What PrEP is and who it is for in Singapore

PrEP is a combination antiretroviral tablet taken by people who are HIV-negative. Held at a steady level in the tissues most exposed during sex, the medication prevents HIV from replicating if it enters the body.

It is generally considered where there is ongoing exposure risk: a partner living with HIV whose virus is not known to be suppressed, condomless sex with partners of unknown status, multiple recent partners, a recent bacterial sexually transmitted infection, or chemsex.¹²

PrEP is prescription-only in Singapore. It is not something to self-source, and it is not something you start without a baseline HIV test, because starting an incomplete regimen while an undiagnosed infection is present risks drug resistance.

Daily oral PrEP: the two combinations

Two tenofovir-based combinations are used for daily PrEP.

Tenofovir disoproxil fumarate with emtricitabine. The longest-standing option, studied across every exposure route, in men who have sex with men, in heterosexual men and women, and in people who inject drugs. It is the only combination with evidence for on-demand dosing.¹²³

Tenofovir alafenamide with emtricitabine. A newer prodrug of tenofovir that produces lower plasma tenofovir levels while achieving similar intracellular levels. In the DISCOVER trial it was non-inferior for HIV prevention in men who have sex with men and transgender women, with more favourable renal and bone density markers and slightly less favourable lipid and weight measures.³ It has not been studied for receptive vaginal exposure and is not used for on-demand dosing.

	Tenofovir disoproxil fumarate with emtricitabine	Tenofovir alafenamide with emtricitabine
Daily dosing	Yes	Yes
On-demand (2-1-1) dosing	Yes, the only studied option	No, no efficacy data
Evidence for receptive vaginal exposure	Yes	Not established
Renal and bone density markers	Small declines seen over time	More favourable in trial data
Lipids and weight	More favourable in trial data	Small increases seen

Which one suits you is a clinical decision that turns on kidney function, bone health, lipid profile, the exposures you actually have, and cost. Both are prescribed and monitored the same way.

On-demand (2-1-1) PrEP

On-demand dosing is event-driven rather than continuous:

• 2 tablets taken 2 to 24 hours before sex
• 1 tablet 24 hours after the first double dose
• 1 tablet 48 hours after the first double dose

If sex continues over several days, the single daily tablet continues until 48 hours after the last episode.

Three points matter more than any other:

1. Only tenofovir disoproxil fumarate with emtricitabine is appropriate for on-demand dosing. Tenofovir alafenamide with emtricitabine has no efficacy data in this schedule and must not be used for it.
2. The on-demand evidence base is in men who have sex with men. It is not established for vaginal exposure, where continuous daily dosing is the appropriate approach.¹²
3. Daily dosing gives more consistent cover. Event-driven dosing depends on correctly anticipating sex and then completing the tail doses. Where sex is frequent or unpredictable, daily dosing is the more forgiving option.

Time to protection, stopping, and adherence

With daily dosing, protective levels are reached at around 7 days of consistent tablets for anal exposure and around 21 days for vaginal exposure. When stopping, daily PrEP is continued for a further 28 days after the last exposure for vaginal exposure, and for at least 2 days after the last exposure for anal exposure. Your doctor will set the exact plan.

Adherence is what determines whether PrEP works. Missed tablets, not the medication itself, are the usual reason protection fails.

Hepatitis B: an important check before you start

Both combinations are active against hepatitis B. If you have chronic hepatitis B and later stop PrEP abruptly, the infection can flare. Hepatitis B status is therefore part of the baseline workup, not an optional extra, and stopping is planned rather than improvised.²

Monitoring while on PrEP

• Before starting: HIV test, hepatitis B status, kidney function, and a full sexually transmitted infection screen
• Every 3 months: HIV test, sexually transmitted infection screen, prescription review
• Periodically: kidney function, with the interval set by your baseline result, age and other medications
• At each review: adherence, side effects, and whether PrEP is still the right tool for your circumstances

Early side effects are usually mild nausea, headache or fatigue in the first few weeks. Serious effects are uncommon.

What PrEP does not cover

PrEP prevents HIV and nothing else. Chlamydia, gonorrhoea, syphilis, herpes and human papillomavirus are unaffected by it. That gap is the reason DoxyPEP exists, and the reason quarterly screening stays in the plan whichever prevention you use. See STD testing and rapid STD testing.

DoxyPEP: doxycycline after sex

DoxyPEP is a single 200 mg dose of doxycycline taken after condomless sex.

Timing is the whole point: ideally within 24 hours, and no later than 72 hours. Do not exceed 200 mg in any 24-hour period.

In the trial evidence, DoxyPEP substantially reduced chlamydia and syphilis. The effect on gonorrhoea is more modest and depends on local doxycycline resistance patterns.⁴⁵

	HIV PrEP	DoxyPEP
Prevents	HIV	Chlamydia and syphilis, partially gonorrhoea
When taken	Before exposure, daily or on-demand	After sex, single dose
Timing	Continuous, or the 2-1-1 schedule	Within 24 hours, no later than 72
Main caveat	Adherence and hepatitis B status	Antimicrobial resistance

Who it is for. The evidence supports DoxyPEP in men who have sex with men and in transgender women, typically where there has been a bacterial sexually transmitted infection in the past 12 months or there are multiple recent partners.⁴⁵⁶ The dPEP-Kenya trial found no benefit in cisgender women, and there is no efficacy data in cisgender heterosexual men, so it is not offered outside the indication above.⁷

Side effects. Doxycycline is usually well tolerated. Nausea, photosensitivity and oesophageal irritation are the common issues. Take it with water and stay upright for 30 minutes afterwards, and use sunscreen.

Resistance. This is the honest caveat. Repeated doxycycline exposure can select for resistant organisms and put pressure on the gut and skin microbiome. Whether DoxyPEP remains appropriate is reviewed at each visit rather than assumed indefinitely.⁸

Using PrEP and DoxyPEP together

They target different pathogens and are commonly used together. Neither replaces regular screening: PrEP does not cover bacterial infections, and DoxyPEP does not cover HIV or the viral infections. Quarterly review is where both are checked, adjusted or stopped.

Access in Singapore

Both are prescription-only. PrEP in Singapore is dispensed as originator tablets; there is no generic version on the local market. Consultation at Hisential is from S$50 after GST, and your personal health concierge coordinates the baseline workup, prescription and quarterly reviews.

Consultations and prescriptions are confidential and are not shared with employers, family or insurers without your consent, except where required by regulations or law.

Buying PrEP online, and what it actually means

Buying either medication from unverified foreign online sources is not advisable because the data that protects you cannot be guaranteed.⁹

Product integrity. A tablet bought online may not contain the correct dose of tenofovir and emtricitabine, may have degraded during storage or transport, or may not be the product it claims to be. Substandard or degraded drug can deliver lower drug levels, which undermines the protection you expect.¹⁰

Clinical gaps. Online supply usually skips the baseline checks that make PrEP safe: an HIV test before starting, hepatitis B status, kidney function, and a full sexually transmitted infection screen. Without these, you may start PrEP while unknowingly HIV-positive, which risks drug resistance, and you have no quarterly data to confirm the strategy is still working.¹⁰

Originator-only context. In Singapore, PrEP is dispensed as originator tablets; there is no generic version on the local market. Products claiming otherwise are unlikely to come through the regulated supply chain.¹¹

What to do instead. Get assessed and prescribed through a licensed clinic so the product, monitoring and counselling are consistent. If you are already sourcing online, arrange baseline testing and quarterly review as soon as possible rather than continuing without oversight.

Frequently asked questions

Can I use tenofovir alafenamide with emtricitabine for on-demand PrEP?

No. On-demand 2-1-1 dosing has only been studied with tenofovir disoproxil fumarate with emtricitabine. There is no efficacy data for tenofovir alafenamide with emtricitabine in this schedule, so it should be used daily or not at all.

How quickly does PrEP start working?

With daily dosing, around 7 days for anal exposure and around 21 days for vaginal exposure. On-demand dosing relies on the double dose taken 2 to 24 hours before sex.

Is on-demand PrEP as good as daily PrEP?

It has strong trial evidence in men who have sex with men, but it is less forgiving. It depends on anticipating sex and completing the tail doses. Daily dosing gives more consistent cover, particularly where sex is frequent or unplanned.

Does DoxyPEP prevent HIV?

No. DoxyPEP is an antibiotic and has no activity against HIV. PrEP or condoms remain the tools for that.

Can women take DoxyPEP?

The evidence does not currently support it. The dPEP-Kenya trial found no reduction in infections among cisgender women, so DoxyPEP is offered to men who have sex with men and transgender women only.

Do I still need testing if I am on both?

Yes. Quarterly HIV testing and a full sexually transmitted infection screen remain part of the plan, and they are what tells you whether the current approach is still working.

What if I have already been exposed to HIV?

PrEP is not the right tool after the fact. If exposure was within the last 72 hours, HIV PEP is the emergency option, and PrEP can follow once that course is complete and HIV-negative status is confirmed.

Related reading

• HIV PrEP at Hisential
• DoxyPEP at Hisential
• HIV testing in Singapore
• STD testing

References

Footnotes

1. Molina JM, et al. On-demand preexposure prophylaxis in men at high risk for HIV-1 infection (IPERGAY). N Engl J Med. 2015. https://pubmed.ncbi.nlm.nih.gov/26624850/ ↩ ↩² ↩³

2. US Centers for Disease Control and Prevention. Preexposure prophylaxis for the prevention of HIV infection in the United States: 2021 update, clinical practice guideline. https://stacks.cdc.gov/view/cdc/112360 ↩ ↩² ↩³ ↩⁴

3. Mayer KH, et al. Emtricitabine and tenofovir alafenamide vs emtricitabine and tenofovir disoproxil fumarate for HIV pre-exposure prophylaxis (DISCOVER). Lancet. 2020. https://pubmed.ncbi.nlm.nih.gov/32711800/ ↩ ↩²

4. Luetkemeyer AF, et al. Postexposure doxycycline to prevent bacterial sexually transmitted infections. N Engl J Med. 2023. https://pubmed.ncbi.nlm.nih.gov/37018493/ ↩ ↩²

5. Molina JM, et al. Doxycycline prophylaxis and meningococcal group B vaccine to prevent bacterial sexually transmitted infections in France (ANRS 174 DOXYVAC). Lancet Infect Dis. 2024. https://pubmed.ncbi.nlm.nih.gov/38797183/ ↩ ↩²

6. US Centers for Disease Control and Prevention. Clinical guidelines on the use of doxycycline postexposure prophylaxis for bacterial sexually transmitted infection prevention. MMWR Recomm Rep. 2024. https://www.cdc.gov/mmwr/volumes/73/rr/rr7302a1.htm ↩

7. Stewart J, et al. Doxycycline prophylaxis to prevent sexually transmitted infections in women. N Engl J Med. 2023. https://pubmed.ncbi.nlm.nih.gov/38118022/ ↩

8. World Health Organization. Pre-exposure prophylaxis (PrEP). https://www.who.int/teams/global-hiv-hepatitis-and-stis-programmes/hiv/prevention/pre-exposure-prophylaxis ↩

9. Health Sciences Authority, Singapore. Consumer safety: buying health products safely. https://www.hsa.gov.sg/consumer-safety ↩

10. HealthHub.sg. Dangers of buying health products online (Health Sciences Authority). https://www.healthhub.sg/well-being-and-lifestyle/personal-care/dangers_health_products_online_hsa ↩ ↩²

11. Health Sciences Authority. HSA joins 84 countries in concerted operation targeting online supply of illegal medicines. https://www.hsa.gov.sg/announcements/hsa-joins-84-countries-in-concerted-operation-targeting-online-supply-of-illegal-medicines/ ↩