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 is not medical advice and does not replace the assessment of an EU-licensed doctor. Your doctor will review your individual history, dose and interactions during your consultation.