References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Amoxicillin is not an effective treatment for chlamydia, gonorrhoea, or most other STIs. If you’re wondering whether you can use leftover amoxicillin to treat a suspected STI, the answer is no. Using the wrong antibiotic won’t clear the infection and can contribute to antibiotic resistance, making future infections harder to treat.
This is a common question, and it makes sense. Amoxicillin is one of the most widely prescribed antibiotics in the UK, and many people have some at home. But STIs require specific antibiotics that target the particular bacteria involved. Here’s what actually works.
Think you might have an STI? Get tested first with a discreet home kit
Why Amoxicillin Doesn’t Work for Most STIs
Amoxicillin is a broad-spectrum penicillin-type antibiotic. It works well for ear infections, chest infections, UTIs, and dental abscesses. But the bacteria that cause the most common STIs have either natural resistance to amoxicillin or require different classes of antibiotics to be effectively killed.
Amoxicillin and chlamydia
Chlamydia trachomatis is an intracellular bacterium, meaning it lives inside your cells. Amoxicillin doesn’t penetrate cells effectively enough to clear a chlamydia infection. The recommended treatments are azithromycin (macrolide class) or doxycycline (tetracycline class), both of which are specifically designed to enter cells and kill intracellular bacteria.
NHS and BASHH guidelines do not recommend amoxicillin for chlamydia at any dose.
Amoxicillin and gonorrhoea
Gonorrhoea (Neisseria gonorrhoeae) has developed significant antibiotic resistance over the past two decades. It is now resistant to most oral antibiotics, including amoxicillin, ciprofloxacin, and tetracyclines. The current recommended treatment is a single injection of ceftriaxone (a cephalosporin), sometimes combined with oral azithromycin.
Using amoxicillin for gonorrhoea would not clear the infection and risks driving further resistance. This is why the UK government monitors gonorrhoea resistance patterns through UKHSA surveillance programmes.
Amoxicillin and syphilis
Syphilis is actually one STI where a penicillin-type drug does work, but the effective treatment is benzathine penicillin G given as an intramuscular injection, not oral amoxicillin tablets. The injection delivers a sustained, high-dose release that oral amoxicillin cannot match. Some guidelines have explored oral amoxicillin as an alternative in specific situations, but it is not standard treatment in the UK.
Which Antibiotics Actually Treat STIs?
| STI | Recommended Treatment (UK/BASHH) | Does Amoxicillin Work? |
|---|---|---|
| Chlamydia | Doxycycline 100mg twice daily for 7 days, or azithromycin 1g single dose | No |
| Gonorrhoea | Ceftriaxone injection (single dose) | No (resistant) |
| Syphilis | Benzathine penicillin G injection | Not recommended (injection required) |
| Trichomoniasis | Metronidazole 400mg twice daily for 5-7 days | No (different organism) |
| Mycoplasma genitalium | Azithromycin followed by moxifloxacin if resistant | No |
| Bacterial vaginosis | Metronidazole 400mg twice daily for 5-7 days | No |
The Problem with Self-Treating STIs
Taking the wrong antibiotic for an STI creates several problems:
- The infection won’t clear — you’ll still be infected and still contagious
- You might think you’re cured — if symptoms happen to improve coincidentally, you may stop seeking proper treatment
- Antibiotic resistance — taking antibiotics unnecessarily or incorrectly helps bacteria develop resistance. Gonorrhoea resistance is already a serious public health concern
- Delayed complications — untreated chlamydia can cause pelvic inflammatory disease and infertility. Untreated syphilis progresses through stages
- You might not have an STI at all — symptoms like discharge, pain, or itching can be caused by UTIs, thrush, or skin conditions. Testing first tells you what you’re actually dealing with
How to Get the Right STI Treatment
The correct process is: test first, then treat based on results.
Step 1: Get tested
You can get tested at a sexual health clinic (free, walk-in), through your GP, or with a home test kit. Testing tells you exactly which infection you have, so you get the right antibiotic.
Step 2: Get prescribed treatment
Once you have a diagnosis, treatment is available through:
- Sexual health clinics — free treatment, often same-day. Find your nearest clinic
- Your GP — can prescribe antibiotics based on test results
- Online prescription services — for confirmed infections
Step 3: Complete the full course
Always finish your antibiotics as prescribed, even if symptoms improve before the course is done. Stopping early increases the risk of resistance and reinfection.
What About Antibiotic Resistance?
STI antibiotic resistance is a growing concern globally. Gonorrhoea in particular has become resistant to most oral antibiotics. The UK’s last-resort treatment is injectable ceftriaxone, and resistance to this drug has been reported in isolated cases internationally.
This is one reason why you should never use leftover antibiotics to self-treat. Using the wrong antibiotic at the wrong dose exposes bacteria to sub-lethal levels of the drug, which is exactly how resistance develops.
Read more: A clear guide to STI antibiotics | Gonorrhoea treatment and resistance
Frequently Asked Questions
Can I use any antibiotic I have at home for an STI?
No. STIs require specific antibiotics. Using the wrong one won’t cure the infection and can contribute to antibiotic resistance. Always get tested and treated with the correct medication.
Can amoxicillin treat a UTI caused by sex?
Amoxicillin can treat some UTIs, but it depends on the bacteria causing the infection. UTIs and STIs are different conditions. If you have symptoms after sex (burning, frequent urination, discharge), get tested for both UTIs and STIs to get the right treatment.
Why do some websites say amoxicillin treats chlamydia?
Some outdated or non-UK sources may reference amoxicillin as an alternative for chlamydia during pregnancy (when doxycycline cannot be used). However, current BASHH and NHS guidelines recommend azithromycin or erythromycin for pregnant women with chlamydia, not amoxicillin.
Is there a single pill that cures all STIs?
No. Different STIs are caused by different organisms and require different antibiotics. There is no universal STI cure. Some infections (herpes, HIV, HPV) are viral and cannot be cured with antibiotics at all.
Can my pharmacist give me STI antibiotics without a prescription?
Not in the UK. STI antibiotics (azithromycin, doxycycline, ceftriaxone) require a prescription. You can get a prescription from your GP, a sexual health clinic, or an online prescriber after a consultation.
Related reading
- Comprehensive Test: Chlamydia, Gonorrhoea and Herpes
- Chlamydia and Gonorrhoea Lab Test
- Home Chlamydia and Gonorrhoea Tests: How They Work
- Rectal Chlamydia and Gonorrhoea Test
- STI Throat Swab for Gonorrhoea and Chlamydia
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
