Safety information · Internal patient-safety page
Doxycycline safety summary
Doxycycline is a tetracycline antibiotic and the standard 7-day treatment for chlamydia. Taken correctly, sitting upright with a full glass of water and with sun protection, it avoids its two classic problems: throat irritation and sunburn-like reactions.
What it's used for
- Swallow each capsule with a full glass of water, sitting or standing upright, and stay upright for at least 30 minutes.
- Take with food or milk to reduce nausea.
- Complete the full 7 days even if symptoms disappear earlier.
- Avoid sex until you have finished the course and any partner has been treated.
Most common side effects
- Nausea, vomiting or diarrhoea.
- Increased sensitivity to sunlight: you burn much faster; avoid strong sun and sunbeds and use high-SPF protection.
- Headache.
- Vaginal or oral thrush after the course.
Serious side effects: stop and seek care
- Pain on swallowing or burning chest pain: the capsule can irritate or ulcerate the oesophagus if it sticks.
- Severe headache with blurred or double vision, a sign of raised pressure around the brain.
- Severe skin reactions, blistering, or an intense sunburn-like reaction.
- Severe or bloody diarrhoea.
- Severe allergic reaction: rash, swelling, difficulty breathing.
Who should not take it
- Pregnant or breastfeeding women: doxycycline deposits in developing bones and permanently stains developing teeth.
- Children under 12, for the same reason.
- Allergy to doxycycline or any other tetracycline.
Interactions to flag
- Antacids and supplements containing calcium, magnesium, aluminium, iron or zinc: separate by 2–3 hours.
- Oral retinoids such as isotretinoin: never combine (risk of raised pressure around the brain).
- Warfarin and similar anticoagulants: effect can be enhanced.
- Some antiepileptics (carbamazepine, phenytoin) and rifampicin lower doxycycline levels.
- Regular heavy alcohol use can shorten the antibiotic's effect.
Message us in the app chat if you notice any of these
- Pain or burning when swallowing.
- Severe headache or any change in vision.
- A blistering or severe sunburn-like skin reaction.
- Symptoms still present after finishing the 7-day course.
AEMPS CIMA: Doxycycline 100 mg
Back to your consultationThis page summarises information from the regulator-approved leaflet for reference only. It does not replace the full leaflet, linked on this page, it is not medical advice and it does not replace the assessment of an EU-licensed doctor. Your doctor will review your individual history, dose and interactions during your consultation.