I took medication for my STI. Am I still contagious?

You can be, for a while. Antibiotics cure bacterial STIs such as Chlamydia and Gonorrhoea, but they need time to work, and your partner needs treatment too. Until then, you could pass the infection on, or catch it straight back.

For infections that can’t be cured, such as Herpes and HIV, treatment lowers the risk of passing them on. With HIV, effective treatment can bring the virus down to a level where you can’t pass it on through sex.

UK guidance for the most common curable STIs is:

• Chlamydia: wait until you’ve finished your treatment and your symptoms have gone. If you were given azithromycin, wait 7 days after treatment.
• Gonorrhoea: wait until 7 days after you and your partner have both finished treatment.
• Syphilis: wait until 2 weeks after you and your partner have finished treatment.
• Trichomonas: wait until at least 1 week after you and your partner have finished treatment.
• Mycoplasma genitalium: wait until 14 days after you started treatment, and until your symptoms have gone.

This includes oral sex. For all of these, your partner should be treated too. Read more in “Can an STI come back after treatment?”

Not always. It depends on the infection:

• Chlamydia: a retest isn’t usually needed. It’s recommended if you’re pregnant, if your symptoms don’t go away, or if you might not have taken all your treatment. It should be at least 3 weeks after you finish treatment, because tests can pick up dead bacteria for a few weeks.
• Gonorrhoea: you’ll usually be offered a follow-up test, and it’s always recommended if the infection was in your throat, which is harder to treat. A test for Gonorrhoea DNA should be at least 2 weeks after treatment.
• Syphilis: you’ll need follow-up blood tests over the first year. Your Syphilis antibody test will usually stay positive for life, even after the infection has been cured, so these checks use a different blood test.
• Trichomonas and Mycoplasma genitalium: a retest is usually only needed if your symptoms don’t go away or come back.

If you’re under 25 and have had Chlamydia, UK guidelines recommend another test 2 to 6 months after treatment, to check you haven’t caught it again. Read more in “How long will I test positive for an STI after treatment?”

Herpes

There’s no cure for Herpes, but outbreaks clear up on their own. It’s very easy to pass on from the first tingle of an outbreak until the sores have healed, so avoid sex during that time. It can also be passed on when there are no symptoms. Taking antiviral medicine every day roughly halves the risk of passing Herpes to a partner, and condoms lower the risk too. Read more in “How long does a Herpes outbreak last?”

HIV

There’s no cure for HIV, but with treatment most people live a long and healthy life. If you’re on effective treatment and have an undetectable viral load, you can’t pass HIV on through sex. It usually takes around 6 months of daily treatment to get there.

HPV and genital warts

There’s no treatment for HPV itself, but most people clear it within 2 years. Treating genital warts removes the warts, not the virus, and HPV can be passed on when there are no visible warts. Condoms lower the risk.

Hepatitis B

Long-term (chronic) Hepatitis B can’t be cured, although antiviral medicine helps to control it. Partners can be protected with the Hepatitis B vaccine.

Most treatment works first time. When a test is still positive, it’s usually because:

• you caught the infection again, from a partner who hasn’t been treated or from a new partner
• you didn’t finish the treatment, or missed doses
• the bacteria are resistant to the antibiotic

Resistance is a growing problem, especially with Gonorrhoea and Mycoplasma genitalium. In England, 15 cases of Gonorrhoea resistant to ceftriaxone, the main treatment, were found in the first 8 months of 2025, more than in the whole of 2024.

If you miss a dose or are sick after taking a tablet, ask the doctor or pharmacist who gave you the treatment what to do.

• Make sure your partner, and any recent partners, are tested and treated. For Chlamydia, that usually means anyone you’ve had sex with in the last 6 months.
• Don’t have sex until the waiting time is up for both of you.
• Use condoms with new or casual partners.
• Get tested when you change partner, and at least once a year if you’re sexually active.

Catching the same infection again is common. Around 10% to 15% of young adults diagnosed with Chlamydia test positive again at a later test. Read more in “Can you tell a partner anonymously they need an STI test?”

If you need a retest, wait the right amount of time after your treatment first. Better2Know offers:

• Peace of Mind: tests for Chlamydia, Gonorrhoea and Syphilis from 14 days after sex, with results in 2 days. You can book it at one of our clinics or order a home test kit.
• Full Screen: tests for 7 infections, including HIV, Syphilis, Chlamydia and Gonorrhoea, from 28 days after sex, with results in 3 days (5 days for the home test).
• Mycoplasma and Trichomonas: urine tests from 14 days after sex, with results in 5 days.

If you’ve had Syphilis before, a standard Syphilis test will usually still be positive, so tell our Patient Care Team when you book. If you test before 45 days, a negative HIV result needs a repeat test. A Syphilis test in the first 3 months after sex can miss the infection, so you may need a repeat test. Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

Can I test straight after finishing treatment?

It’s best to wait. After Chlamydia treatment, tests can pick up dead bacteria for 3 to 5 weeks, so testing too soon can give a positive result even when the infection has gone.

Does my partner need treatment if their test is negative?

Sometimes, yes. For Trichomonas, for example, UK guidelines say current partners should be treated whatever their test result.

Will I always test positive for Syphilis?

Usually, on the antibody test. That doesn’t mean you still have Syphilis. Doctors use a different blood test to check the treatment has worked.

Treatment works for most STIs, but it isn’t an instant switch. Give it time to work, make sure your partner is treated too, and wait the recommended time before having sex again. If you’re not sure whether an infection has gone, or you’ve had a new partner since, a test will tell you.

Book a Peace of Mind test at a clinic near you or order a home test kit. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 3 November 2023 and was last updated on 1 October 2026.

Medical review. This article was medically reviewed by Dr Steve Chapman, Doctor with a wealth of clinical experience in the field of STIs, on 13 July 2026. It is general information and not a substitute for personal medical advice.

Sources

1. NHS, Chlamydia, reviewed 24 October 2024. https://www.nhs.uk/conditions/chlamydia/
2. British Association for Sexual Health and HIV, UK national guideline for the management of infection with Chlamydia trachomatis, 2026. https://www.bashh.org/_userfiles/pages/files/national_guideline_for_the_management_of_infection_chlamydia_trachomatis_2026.pdf
3. NHS, Gonorrhoea, reviewed 16 December 2024. https://www.nhs.uk/conditions/gonorrhoea/
4. British Association for Sexual Health and HIV, UK national guideline for the management of infection with Neisseria gonorrhoeae, 2025. https://www.bashh.org/_userfiles/pages/files/fiferetal2025britishassociationofsexualhealthandhivuknationalguidelineforthemanagementofinfection_1.pdf
5. UK Health Security Agency, GRASP report: data to September 2025, updated 18 December 2025. https://www.gov.uk/government/publications/gonococcal-resistance-to-antimicrobials-surveillance-programme-grasp-report/grasp-report-data-to-september-2025
6. NHS, Syphilis, reviewed 17 March 2026. https://www.nhs.uk/conditions/syphilis/
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8. NHS, Trichomoniasis, reviewed 16 July 2025. https://www.nhs.uk/conditions/trichomoniasis/
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11. NHS, Genital herpes, reviewed 27 June 2023. https://www.nhs.uk/conditions/genital-herpes/
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13. NHS, HIV and AIDS, reviewed 9 July 2025. https://www.nhs.uk/conditions/hiv-and-aids/
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