Several evidence-based strategies can lower your risk of sexually transmitted infections without relying on condoms, and a few of them are remarkably effective. Vaccines, prescription prophylaxis drugs, suppressive antiviral therapy, and even a post-sex antibiotic are all backed by clinical trial data showing meaningful reductions in specific infections. None of these tools protects against every STI the way a condom can, and some remain limited to certain populations or pathogens, so the practical question is less “condom or not” and more “which combination of strategies fits your life and risk profile.”
Vaccines That Block STIs Before They Start
Vaccination is the closest thing to a set-and-forget prevention method. Three STIs already have effective vaccines, and a fourth is showing unexpected promise through a vaccine originally designed for a different disease entirely.
The HPV vaccine is the biggest success story. In men who had not yet been exposed to the targeted virus strains, the quadrivalent vaccine showed long-term efficacy above 90% against HPV-related external genital lesions over a decade of follow-up, and it durably reduced detection of DNA from the four vaccine-targeted HPV types.1PubMed Central. Efficacy of human papillomavirus vaccines in the prevention of male genital diseases: a systematic review In women, the vaccine’s impact on genital warts has been dramatic. A meta-analysis of randomized trials found a roughly 97% reduction in genital warts among young vaccinated women, with population-level time-trend analyses showing benefits extending to young men through herd effects.2PubMed Central. The quadrivalent HPV vaccine is protective against genital warts: a meta-analysis HPV vaccination also reduces the strains responsible for cervical, anal, and oropharyngeal cancers. If you were not vaccinated as a teenager, catch-up vaccination is available through age 26 in most guidelines and sometimes older.
Hepatitis B is another sexually transmissible infection that vaccination has largely defanged. The WHO has recommended universal HBV immunization since 1991, and mass vaccination programs have dramatically lowered both infection rates and liver cancer incidence in countries that adopted them.3PubMed Central. Epidemiology and Prevention of Hepatitis B Virus Infection Hepatitis A, which can also spread through sexual contact, is similarly preventable by vaccination.4PubMed Central. Sexual transmission and prevention of the hepatitis viruses A-E and G
An unexpected development has been the observation that a meningococcal B vaccine appears to offer partial cross-protection against gonorrhea. A systematic review and meta-analysis of eight studies estimated a pooled vaccine effectiveness of about 32% against gonorrhea after at least one dose, with individual study estimates ranging from 23% to 47%.5The Journal of Infectious Diseases. Effectiveness of MenB-4C Vaccine Against Gonorrhea: A Systematic Review and Meta-analysis One study in Southern California found gonorrhea rates were 46% lower among recipients of the MenB vaccine compared with a control group, while chlamydia rates were unaffected, supporting the idea that the protection is specific to the shared biology between the meningococcal and gonococcal bacteria.6Clinical Infectious Diseases. Prevention of Neisseria gonorrhoeae With Meningococcal B Vaccine: A Matched Cohort Study in Southern California A 32% reduction is modest, but gonorrhea currently has no dedicated vaccine, so this incidental benefit from an existing shot is significant. Research groups are now investigating vaccines designed specifically for gonorrhea.
HIV Pre-Exposure Prophylaxis
Pre-exposure prophylaxis, or PrEP, has transformed HIV prevention. When taken consistently, a daily pill containing tenofovir disoproxil fumarate and emtricitabine provides extremely high protection against HIV. How much protection depends almost entirely on how regularly you take it. In trials where adherence exceeded 70%, PrEP cut the risk of acquiring HIV by about 70%.7PubMed Central. Effectiveness and safety of oral HIV preexposure prophylaxis for all populations In trials where adherence was low, the protective effect largely disappeared. The drug needs to be in your system to work, which sounds obvious but matters because real-world pill-taking is uneven. Even at 50% adherence, the pattern of missed doses affects how much protection remains, with periodic gaps being less harmful than long unprotected stretches.8PubMed Central. PrEP adherence patterns strongly impact individual HIV risk and observed efficacy in randomized clinical trials
For cisgender women, the adherence-efficacy relationship has been harder to pin down. An analysis that combined data from three major trials estimated that taking two pills per week reduced HIV incidence by about 59%, four pills per week by roughly 84%, and daily use by about 96%.9PubMed Central. Efficacy estimates of oral pre-exposure prophylaxis for HIV prevention in cisgender women with partial adherence The takeaway is straightforward: PrEP works extraordinarily well when taken consistently, and even imperfect use provides meaningful, dose-dependent benefit.
Long-Acting Injectable PrEP
If daily pills are a barrier, injectable PrEP offers an alternative that removes the adherence problem almost entirely. Cabotegravir, given as an injection every two months, has been shown to prevent more infections than daily oral PrEP at similar usage levels.10PubMed Central. Estimating the impact of HIV PrEP regimens containing long-acting injectable cabotegravir or daily oral tenofovir disoproxil fumarate/emtricitabine among men who have sex with men in the United States: a mathematical modelling study for HPTN 083 Modeling studies suggest that at a 35% coverage level among men who have sex with men, injectable PrEP could avert about 44% of new HIV infections, compared with 33% for oral PrEP, primarily because the injection eliminates the daily compliance challenge.11The Lancet HIV. Relative effectiveness and population-level impact of long-acting injectable pre-exposure prophylaxis for HIV prevention among men who have sex with men in Atlanta, GA, USA: a modelling study
Even newer is lenacapavir, a twice-yearly injection. In the PURPOSE 1 trial among women, injectable lenacapavir was 100% efficacious over 52 weeks: not a single participant receiving the drug acquired HIV. Compared with no PrEP use, lenacapavir was 96% efficacious in the PURPOSE 2 trial.12PubMed Central. Clinical Recommendation for the Use of Injectable Lenacapavir as HIV Preexposure Prophylaxis — United States, 2025 A shot every six months that essentially eliminates the risk of HIV acquisition is a dramatic step forward. It was recommended by the CDC in 2025 and is beginning to become available, though cost and access remain barriers for many people.
Doxycycline After Sex for Bacterial STIs
One of the most talked-about recent developments is doxycycline post-exposure prophylaxis, commonly called doxy-PEP. The idea is simple: take 200 mg of doxycycline within 72 hours after condomless sex to prevent bacterial STIs. Across three large randomized trials, this approach reduced syphilis and chlamydia infections by more than 70% and gonococcal infections by roughly 50%.13Morbidity and Mortality Weekly Report. CDC Clinical Guidelines on the Use of Doxycycline Postexposure Prophylaxis for Bacterial Sexually Transmitted Infection Prevention, United States, 2024
The DoxyPEP trial, published in the New England Journal of Medicine, was among the most striking. Among men on HIV PrEP who took doxycycline after sex, the overall STI rate per quarterly visit dropped from about 32% in the standard-care group to roughly 11%. Protection against chlamydia was especially strong, with an 88% reduction, and syphilis infections dropped by about 87%. Gonorrhea was also significantly reduced, though to a lesser degree.14PubMed Central. Postexposure Doxycycline to Prevent Bacterial Sexually Transmitted Infections Real-world data from a public STD clinic in Philadelphia confirmed these findings, showing a 62% overall reduction in STI rates among doxy-PEP users, with chlamydia dropping by about 72% and gonorrhea by about 51%.15PubMed Central. Doxycycline post-exposure prophylaxis is effective and highly acceptable in an urban public sexually transmitted disease clinic: Philadelphia, 2019–2023
Doxy-PEP is currently recommended by the CDC for men who have sex with men and transgender women who have had a bacterial STI in the past year or are at otherwise elevated risk. There are genuine concerns about antibiotic resistance. One trial found that about a quarter of positive gonorrhea cultures showed tetracycline resistance regardless of whether the participant was taking doxy-PEP, suggesting that existing resistance is already common, though widespread doxycycline use could still push rates higher.16The Lancet Infectious Diseases. Doxycycline post-exposure prophylaxis for the prevention of bacterial sexually transmitted infections: a randomized trial The CDC guidelines weigh this risk against the benefits and currently endorse the approach for high-risk populations, while noting the need for ongoing resistance monitoring.
Suppressive Therapy for Herpes
Genital herpes is one of the hardest STIs to prevent because the virus sheds from skin even when there are no visible sores. Daily antiviral medication taken by the infected partner substantially reduces both shedding and transmission risk. In a landmark trial of serodiscordant couples, daily valacyclovir cut the risk of transmitting HSV-2 by about 48% overall and reduced symptomatic herpes acquisition in the uninfected partner by 75%.17PubMed. Once-daily valacyclovir to reduce the risk of transmission of genital herpes The mechanism is straightforward: antiviral therapy dramatically reduces how often the virus appears on genital skin. In that same trial, the infected partners shed HSV DNA on about 3% of days while on valacyclovir versus about 11% of days on placebo.
Higher doses provide even more suppression. A crossover study comparing different regimens found that standard-dose acyclovir reduced shedding to just over 1% of days, compared with about 18% with no medication. Higher doses of valacyclovir further reduced shedding compared with standard doses.18The Lancet. Effect of different doses of aciclovir and valaciclovir on genitally-shed herpes simplex virus type 2: a crossover study There is an important caveat: in people co-infected with both HSV-2 and HIV, daily acyclovir did not significantly reduce HSV-2 transmission to their partners, possibly because immune suppression complicates the picture.19The Journal of Infectious Diseases. Daily Acyclovir to Decrease Herpes Simplex Virus Type 2 (HSV-2) Transmission from HSV-2/HIV-1 Coinfected Persons: A Randomized Controlled Trial For most serodiscordant couples, though, suppressive therapy is a well-established tool that meaningfully lowers transmission risk.
Post-Exposure Prophylaxis for HIV
If you may have been exposed to HIV, a 28-day course of antiretroviral drugs started within 72 hours of exposure can prevent the virus from establishing an infection. This is called non-occupational post-exposure prophylaxis, or nPEP. The evidence base rests primarily on non-human primate studies and observational human data rather than randomized trials, because assigning a placebo to someone who may have been exposed to HIV would be unethical. Those primate studies consistently showed that the sooner treatment began after exposure, the better it worked, and that protection dropped sharply after the 72-hour window.20Morbidity and Mortality Weekly Report. Antiretroviral Postexposure Prophylaxis After Sexual, Injection Drug Use, or Other Nonoccupational Exposure to HIV — CDC Recommendations, United States, 2025 Current CDC guidelines recommend nPEP for anyone without HIV who seeks care within 72 hours of a nonoccupational exposure that carries substantial risk, and emphasize that earlier initiation is better.21PubMed Central. Current perspectives in HIV post-exposure prophylaxis
nPEP is an emergency measure, not a routine strategy. The month-long drug course can have side effects, and it requires prompt access to a healthcare provider. But for the occasional high-risk exposure, it is an important safety net.
Undetectable Equals Untransmittable
If your sexual partner is living with HIV and their viral load is consistently undetectable on antiretroviral therapy, they cannot transmit HIV sexually. This principle, known as U=U, is supported by strong evidence from large studies of serodiscordant couples and has been endorsed by the CDC, NIH, and major medical organizations worldwide.22JAMA. HIV Viral Load and Transmissibility of HIV Infection: Undetectable Equals Untransmittable U=U is not a probabilistic reduction in risk. It means zero transmissions in tens of thousands of condomless sex acts studied. For couples where one partner is HIV-positive and virally suppressed, this is the single most reassuring piece of evidence in all of STI prevention.
Male Circumcision
Three large randomized trials conducted in sub-Saharan Africa established that voluntary male circumcision reduces a man’s risk of acquiring HIV through vaginal sex by roughly 50% to 60% over time. It also lowers the risk of acquiring HSV-2 and HPV by about 30%.23PubMed Central. Male circumcision and Sexually transmitted Infections – An update The biological explanation centers on the foreskin’s thin mucosal surface and high density of immune cells that HIV targets. Removing that tissue reduces the vulnerable surface area.
The evidence is strongest for heterosexual men in high-prevalence settings. It is less clear how much circumcision helps in low-prevalence populations or during receptive anal sex. Circumcision is a one-time, permanent intervention, which makes it appealing from a public-health perspective, but it is partial protection, not a substitute for other tools.
The Dapivirine Vaginal Ring
For women in areas with high HIV prevalence, a monthly vaginal ring releasing the antiretroviral drug dapivirine offers a discreet, self-managed prevention option. Two Phase 3 trials showed that the ring reduced HIV acquisition by about 27% to 31% compared with placebo.24PubMed. Use of a Vaginal Ring Containing Dapivirine for HIV-1 Prevention in Women25PubMed. Safety and Efficacy of a Dapivirine Vaginal Ring for HIV Prevention in Women That headline number is underwhelming compared with oral PrEP, but there is important context. In women over 21 who used the ring more consistently, one trial found 56% protection. Among younger women, adherence was much lower and protection disappeared. When the ring was offered in an open-label extension and women chose to use it knowing what it was, about 73% used it at every visit, and HIV incidence dropped to 2.7 per 100 person-years compared with an expected 4.4 among a matched group.26The Lancet HIV. Use and safety of the dapivirine vaginal ring in an open-label extension trial in African women The ring was approved by the WHO and the European Medicines Agency and fills a gap where oral PrEP faces uptake challenges. With injectable lenacapavir now entering the picture, the ring may ultimately be one choice among several long-acting options.
What Does Not Work
Some widely believed prevention strategies are either useless or actively harmful. Clearing these up matters because people who rely on ineffective methods are taking on more risk than they realize.
Nonoxynol-9, a spermicide once marketed as having antimicrobial properties, does not protect against HIV or other STIs. A Cochrane review of five high-quality randomized trials found no significant reduction in HIV, gonorrhea, chlamydia, or any other STI among women using nonoxynol-9 products. Worse, women who used nonoxynol-9 had a significantly higher rate of genital lesions, which could paradoxically increase vulnerability to infection.27PubMed Central. Nonoxynol‐9 for preventing vaginal acquisition of HIV infection by women from men28PubMed. Nonoxynol-9 spermicide for prevention of vaginally acquired HIV and other sexually transmitted infections: systematic review and meta-analysis of randomised controlled trials including more than 5000 women
Vaginal douching is another practice that increases rather than decreases risk. A prospective study of adolescents found that those who always douched were about twice as likely to acquire an STI compared with those who never douched, even after adjusting for other risk factors.29PubMed Central. Does douching increase risk for sexually transmitted infections? A prospective study in high-risk adolescents Douching disrupts the vaginal microbiome and mucosal barriers in ways that leave tissue more vulnerable to pathogens.
Serosorting, the practice of choosing sexual partners based on reported HIV status, reduces risk somewhat compared with having unprotected sex with partners of unknown status. But it is far less protective than either condom use or PrEP. A meta-analysis found that serosorting was associated with about 80% higher odds of HIV acquisition compared with consistent condom use, while still being better than no precaution at all.30PubMed Central. Serosorting and HIV/STI Infection among HIV-Negative MSM and Transgender People: A Systematic Review and Meta-Analysis to Inform WHO Guidelines The problem is that serosorting depends on accurate, recent knowledge of a partner’s status, which is undermined by infrequent testing, nondisclosure, and the high infectiousness of very recent infections that even the infected person may not know about.31PubMed Central. A strategy for selecting sexual partners believed to pose little/no risks for HIV: serosorting and its implications for HIV transmission
Partner Treatment and Rapid Testing
Prevention is not just about what you do to your own body. Getting sexual partners treated quickly has a measurable effect on reinfection. Expedited partner therapy, where a clinician provides medication or a prescription for a patient’s sex partner without requiring the partner to come in for a visit, has been studied in clinical trials and real-world programs. A randomized trial found that expedited partner therapy reduced persistent or recurrent gonorrhea or chlamydial infection from 13% to 10%, with the effect being strongest for gonorrhea specifically, where reinfection dropped from 11% to 3%.32PubMed. Effect of expedited treatment of sex partners on recurrent or persistent gonorrhea or chlamydial infection Multiple evaluations have consistently shown that this approach increases the proportion of partners who actually get treated, though the downstream effect on community-wide infection rates has been harder to demonstrate.33PubMed Central. Expedited partner therapy for sexually transmitted infections
Rapid point-of-care testing is a related structural tool. When people can get tested and treated in the same visit, it interrupts transmission chains that otherwise persist while someone waits days for lab results.34PubMed Central. Point-of-Care Testing for Sexually Transmitted Infections: A Review of Recent Developments Frequent testing does not prevent infection directly, but it shortens the period during which someone can unknowingly pass an STI to others.
Experimental and Emerging Approaches
Several strategies are in earlier stages of research and not yet part of routine recommendations, but they hint at what prevention might look like in the near future.
Broadly neutralizing antibodies against HIV are being tested as a form of passive immunization. The idea is to infuse someone with antibodies that can block a wide range of HIV strains. In the first large-scale efficacy trials, a single antibody called VRC01 was about 75% effective at preventing infection with HIV strains that were sensitive to it. The problem was that many circulating HIV strains were not sensitive, so the overall protection was not high enough to be practical.35PubMed. Two Randomized Trials of Neutralizing Antibodies to Prevent HIV-1 Acquisition Newer trials are testing combinations of two or three antibodies that together cover a much broader range of HIV variants.36PubMed Central. Broadly Neutralizing Antibodies for HIV-1 Prevention If those combination approaches work, a long-acting antibody infusion could become another option alongside injectable PrEP.
Mouthwash for pharyngeal gonorrhea is an intriguing but unresolved idea. A small randomized trial found that men who gargled with an antiseptic mouthwash were significantly less likely to have gonorrhea detectable on their throat surface immediately afterward, with culture positivity dropping from 84% in the saline group to 52% in the mouthwash group.37Sexually Transmitted Infections. Antiseptic mouthwash against pharyngeal Neisseria gonorrhoeae: a randomised controlled trial and an in vitro study But whether that translates into fewer actual infections is unclear. A mathematical modeling study found that the outcome depends on a tricky biological question: if mouthwash kills bacteria that are already in the throat but also irritates tissue enough to make new infection easier, the net effect could go either way.38PubMed Central. Potential effect of antiseptic mouthwash on the incidence of Neisseria gonorrhoeae among men who have sex with men: a mathematical modelling study Lab data shows that different mouthwashes vary widely in their ability to inhibit gonorrhea bacteria, and saliva itself changes how well they work.39PubMed Central. Inhibitory Activity of Antibacterial Mouthwashes and Antiseptic Substances against Neisseria gonorrhoeae It is too early to recommend this as a prevention strategy, but the research is active.
Vaginal microbiome therapies represent yet another frontier. A Phase 2b trial of LACTIN-V, a live biotherapeutic containing Lactobacillus crispatus given after standard treatment for bacterial vaginosis, showed sustained reductions in genital inflammation and improvements in a biomarker of tissue integrity.40The Lancet Microbe. Effect of a live biotherapeutic containing Lactobacillus crispatus CTV-05 (LACTIN-V) on genital immunology and the vaginal microbiota: a randomised, placebo-controlled, phase 2b substudy The hypothesis is that restoring a healthy lactobacillus-dominant vaginal microbiome could make the tissue more resistant to HIV and other infections. This is still firmly in the investigational stage, but it reflects a growing understanding that the microbial ecosystem of the genital tract is itself a form of defense.