STI testing and treatment: what to expect
In my years as a GP, I've seen how anxiety around STI testing stops people from getting help.
Here is my honest, practical guide to testing, treatments like Aciclovir, and protecting your health.
Rates of sexually transmitted infections in England reached record levels in the most recent UKHSA surveillance reports, with gonorrhoea diagnoses at their highest since reporting began in 1918 and syphilis continuing its post-pandemic rise.
Against that backdrop, the British testing and treatment pathway has quietly become one of the best in the world, combining NHS sexual health clinics, home self-sampling kits, GP services and regulated private online care.
The practical challenge for most people is not access but knowing which test, when, and what to do about a positive result.
When should you test, and for what?
The short answer, from NHS guidance on STIs, is that anyone sexually active with new or multiple partners should test at least annually, and more often when partners change frequently. The testing menu varies slightly by risk profile, but a comprehensive UK check typically includes chlamydia, gonorrhoea, HIV and syphilis, with hepatitis B added for men who have sex with men and people from countries with higher prevalence, and hepatitis C added for anyone with injecting drug use history.
Window periods you actually need to remember
The window period is the time between exposure and the earliest reliable detection by current UK assays. Testing too early gives a falsely reassuring negative. Practical windows:
- Chlamydia and gonorrhoea by NAAT: 2 weeks after exposure
- HIV by 4th-generation antigen-antibody test: 45 days, with most infections detectable from day 18 to 28
- Syphilis by treponemal IgG/IgM: 12 weeks from exposure for definitive reassurance, though most cases become positive within 6 weeks
- Hepatitis B surface antigen: 6 weeks to 6 months depending on viral load
- Hepatitis C antibody: 3 months
Because windows overlap imperfectly, UK sexual health services usually recommend testing immediately if symptomatic, then a full repeat screen at 12 weeks after the most recent possible exposure for complete reassurance.
How UK testing actually works in 2026
Three parallel routes exist and all are free or low cost:
- NHS sexual health clinic (GUM clinic or integrated sexual health service). Walk-in or bookable, usually same or next day. Full examination available, best for symptomatic or complex cases.
- Free home testing kits from local authority commissioned services (available in most English and Welsh regions via sh24, SHL or similar). Self-collected urine, swab and finger-prick blood posted to the lab, results by SMS typically within 3 working days.
- GP practice. Can test for most STIs but less convenient for partner notification and follow-up than dedicated services.
Private online STI testing services provide the same assays but with faster turnaround and more flexible hours, usually charging 40 to 150 pounds for a full screen.
Partner notification: why it matters
If you test positive, UK services offer confidential partner notification, either through the clinic contacting partners anonymously or through you directly using a service such as sxt.org.uk. This is not optional thinking: untreated partners reinfect, antibiotic resistance is driven by incomplete treatment of sexual networks, and the public health justification for fully contact-traced pathways is as strong now as it has ever been. Patient Info's overview of sexually transmitted infections explains the process in patient-friendly language.
Symptoms that should prompt immediate testing
Most STIs are asymptomatic, which is exactly why screening matters. When symptoms do occur, they are clinically meaningful and should not be ignored. See a clinician urgently if you have:
- Unusual discharge from the penis, vagina or anus
- Pain, burning or stinging on passing urine
- Lumps, blisters, sores, warts or ulcers in the genital, anal or oral region
- Rash on the palms or soles (classic secondary syphilis)
- Unexplained pelvic pain, bleeding between periods or after sex
- Painful, swollen testicles
- Flu-like illness with sore throat and rash 2 to 4 weeks after risk exposure (possible HIV seroconversion)
First-line treatments in the UK, infection by infection
Chlamydia
First-line UK treatment for uncomplicated genital chlamydia in adults is doxycycline 100 mg twice daily for 7 days, following the updated BASHH 2024 guidelines which moved away from single-dose azithromycin as first line because of concerns around resistance and incomplete eradication at extragenital sites. Azithromycin remains an option in pregnancy. A test of cure is recommended at 3 to 6 weeks for rectal chlamydia and during pregnancy.
Gonorrhoea
First-line UK treatment is ceftriaxone 1 g intramuscularly as a single dose, administered in a clinic setting because of concerns about rising resistance.
Oral regimens are no longer recommended first line. This is one infection where online prescribing cannot fully substitute for a clinic visit.
Test of cure at 2 weeks is mandatory.
Syphilis
Treated with benzathine penicillin intramuscularly, dosed according to stage (single dose for early syphilis, three weekly doses for late or latent of unknown duration). Again, this is clinic-administered. Doxycycline 100 mg twice daily for 14 to 28 days is the penicillin-allergic alternative.
Genital herpes
First episodes are treated with aciclovir 400 mg three times daily for 5 days, ideally started within 72 hours of lesion onset. Recurrent episodes benefit from episodic therapy at the first sign of prodrome, or suppressive daily aciclovir 400 mg twice daily if recurrences exceed 6 per year. Topical aciclovir cream has a limited evidence base for genital herpes and is generally not recommended; oral treatment is the standard of care.
Trichomoniasis and bacterial vaginosis
Both are treated with metronidazole 400 to 500 mg twice daily for 5 to 7 days, or a single 2 g dose in specific circumstances.
Bacterial vaginosis is not technically an STI but commonly presents alongside STI symptoms and is therefore covered in the same pathway.
Human papillomavirus and genital warts
Warts are treated topically (podophyllotoxin or imiquimod) or by cryotherapy in clinic. HPV itself clears spontaneously in 90% of cases within 2 years; routine cervical and, in some services, anal screening follows UKHSA and NHS cervical screening programme intervals.
HIV
A positive HIV test is no longer the diagnosis it was.
Current UK practice is rapid initiation of antiretroviral therapy within days of diagnosis, with the goal of undetectable viral load within weeks.
Undetectable equals untransmittable (U=U) is the evidence-based public health message.
HIV care is delivered through specialist NHS services; pre-exposure prophylaxis (PrEP) is available free through sexual health services for eligible individuals.
What a good STI consultation feels like
Whether you walk into a GUM clinic, book an online appointment, or order a home kit, a quality UK STI consultation covers the same ground: a non-judgemental sexual history, the specific exposures that guide which tests to run, window period calculation, appropriate specimen collection or prescription, and clear aftercare including partner notification and when to retest. Regulated online services are governed by the MHRA and CQC; the MHRA website is the authoritative source for verifying a provider's legitimacy.
When online prescribing is appropriate, and when it is not
Online prescribing works well for asymptomatic screening, recurrent genital herpes, known partner contacts needing epidemiological treatment, and follow-up test-of-cure prescriptions. It does not replace in-person care for suspected pelvic inflammatory disease, disseminated gonococcal infection, primary syphilis with ulcer, or any infection requiring intramuscular therapy. Use the antibiotics, antivirals and infections categories to see UK-licensed options with their full summary of product characteristics.
Prevention, vaccination and routine screening
The best STI is the one you never acquire. UK prevention tools in 2026 include:
- Condoms: still the most effective barrier for most STIs, particularly gonorrhoea, chlamydia, HIV and syphilis.
- PrEP: free through NHS sexual health services for eligible people at substantial ongoing HIV risk.
- HPV vaccination: offered to all school-age children and to men who have sex with men up to age 45 through sexual health services.
- Hepatitis B vaccination: universal since 2017 for infants; available to adults through clinics for risk groups.
- Doxy-PEP: post-exposure prophylaxis with single-dose doxycycline within 72 hours of unprotected sex, now recommended by some UK services for eligible men who have sex with men to reduce bacterial STI incidence. Discuss with a sexual health specialist.
- Regular screening: 3-monthly for those on PrEP, 6 to 12-monthly for most sexually active adults with changing partners.
STI testing has never been quicker, cheaper or more private in the UK.
If there is a practical takeaway from the numbers in this year's UKHSA data, it is simply to test when in doubt, treat fully when positive, notify partners honestly, and rebook the next screen before you leave the consultation.
A ten-minute conversation and a swab cost nothing and change the course of a silent infection that, left alone, would change rather more.
Commonly asked questions about UK STI testing and treatment
How long after treatment am I safe to have sex again?
For chlamydia treated with doxycycline, UK guidance is to avoid sex, including oral and anal, for 7 days after starting treatment, and until any current partners have also completed treatment.
For gonorrhoea, the rule is 7 days after the ceftriaxone injection. For syphilis, abstain until serological evidence of treatment response is confirmed.
For genital herpes, avoid skin-to-skin genital contact during prodrome and active lesions; suppressive therapy reduces but does not eliminate asymptomatic shedding, so condoms remain important even when lesion-free.
Do I need to tell my current partner if I tested positive?
Yes, and UK services will support you to do so either directly or anonymously. Partner notification is not a moral issue: it is a clinical one.
Untreated partners become reinfection sources, drive antibiotic resistance, and in the case of HIV or syphilis risk onward transmission with serious consequences.
Services such as sxt.org.uk send anonymised SMS or email notifications that name the infection but not the index patient, which removes most of the awkwardness from the process.
Can I just buy antibiotics online for an STI without testing?
No, and you should be wary of any service that offers this.
UK regulated prescribers require either a positive test result or a confirmed partner notification (epidemiological treatment) before issuing antibiotics for STIs.
Empirical antibiotics without diagnosis drive resistance, mask other infections, and miss atypical presentations.
The right pathway is always test first, treat based on result, and retest where clinically indicated.
What does doxy-PEP actually involve?
Doxy-PEP (post-exposure prophylaxis with doxycycline) means taking 200 mg of doxycycline as a single dose within 72 hours of unprotected sex to reduce the risk of subsequent chlamydia, gonorrhoea and syphilis.
Current UK recommendations, informed by the 2024 BASHH position statement, suggest offering doxy-PEP to men who have sex with men and transgender women with a recent history of bacterial STI or multiple partners, as part of a shared decision with a sexual health specialist.
It is not routinely recommended for cis-gender heterosexuals based on current evidence.