Doxycycline

Is doxycycline safe?

Yes, for most adults and older children. Doxycycline is a tetracycline antibiotic that has been prescribed since 1967 for chest infections, acne and rosacea, Lyme disease and other tick-borne infections, chlamydia and syphilis, and malaria prevention for travellers. Serious reactions are rare, overdose is not a major worry, and there is no dependence.

Its problems are practical rather than dangerous. It makes skin burn faster in the sun. It can ulcerate the gullet if swallowed lying down. Antacids, calcium, magnesium and iron can stop it being absorbed. And it can stain teeth in young children. We score it 86, between amoxicillin (91) and ciprofloxacin (64).

What is the usual dose of doxycycline?

Doses from the US doxycycline hyclate label (other forms such as Doryx MPCMPC walletA crypto wallet that splits the private key into several shares held in different places, so no single device or company holds the whole key.More in the glossary are not interchangeable mg for mg):

Use	Dose
Most infections, adults	200 mg on day 1 (100 mg every 12 hours), then 100 mg a day
Severe infections	100 mg every 12 hours
Chlamydia, non-gonococcal urethritis	100 mg twice a day for 7 days
Early syphilis (penicillin allergy)	100 mg twice a day for 2 weeks
Malaria prevention, adults	100 mg once a day, from 1 to 2 days before travel until 4 weeks after leaving; no more than 4 months
Children under 45 kg, severe infections	2.2 mg per kg every 12 hours
Rosacea (Oracea capsule)	40 mg once a day in the morning

Finish the course your prescriber gives you, even if you feel better.

Sunburn and throat ulcers: the common problems

Photosensitivity. Some people get an exaggerated sunburn after short sun exposure. The label says to avoid strong sunlight and sunbeds, consider sunscreen, and stop at the first sign of skin redness. Travellers on daily malaria tablets in the tropics are the group most exposed.

The gullet. Tablets and capsules that lodge in the oesophagus can cause painful ulcers. Most reported cases took the drug right before bed. The NHS advice: swallow it whole with a full glass of water while sitting or standing, and stay upright for at least 30 minutes. Pain on swallowing or behind the breastbone is a reason to call your doctor.

Nausea is common, and taking it with food or milk can help; unlike older tetracyclines, the label says food and milk do not markedly cut absorption.

Interactions: minerals, isotretinoin and warfarin

The main interaction blocks the antibiotic rather than harming you. Doxycycline binds to metal ions in the gut, so antacids with aluminium, calcium or magnesium, iron tablets and bismuth (Pepto-Bismol) reduce how much gets absorbed. Calcium and magnesium supplements, and zinc, do the same. A pharmacist can tell you how to space them.

The more serious one is isotretinoin. Both drugs can raise the pressure inside the skull (intracranial hypertension, or pseudotumor cerebri), with headache, blurred or double vision and, rarely, permanent vision loss. The label says to avoid the combination, which matters because both treat acne. Women of childbearing age who are overweight or have had the condition before are at higher risk.

Other label interactions: warfarin may need a lower dose; carbamazepine, phenytoin and barbiturates shorten doxycycline's action; the anaesthetic methoxyflurane caused fatal kidney damage with tetracyclines; and the label says tetracyclines may make contraceptive pills less effective.

Rare but serious reactions

Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis and DRESS) have been reported; the warning was strengthened in March 2025 to include fixed drug eruptions that get worse each time the drug is taken. Stop and get urgent help for a spreading rash with blisters, fever or peeling skin. Like other antibiotics, doxycycline can trigger C. difficile diarrhoea, sometimes weeks after the course ends. Liver injuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary, pancreatitis and blood disorders are rare.

Children, pregnancy and doxy-PEP

US labels restrict use under age 8 to severe or life-threatening infections, because tetracyclines can permanently stain developing teeth yellow-grey-brown. The CDC goes further for Rocky Mountain spotted fever, recommending doxycycline at any age, including in pregnancy, because delayed treatment can be fatal. In pregnancy more generally, a doctor weighs the infection against tooth and bone effects.

Doxycycline is also used after sex to prevent STIs. In 2024 the CDC recommended counselling gay and bisexual men and transgender women who had syphilis, chlamydia or gonorrhoea in the past year about doxy-PEP: 200 mg within 72 hours of condomless sex. This is a prescribed strategy with follow-up testing, not something to start alone.

Who should be careful

Talk to your doctor or pharmacist before taking doxycycline if you take isotretinoin, warfarin, seizure medicines or iron, calcium or antacids, are pregnant or breastfeeding, have liver disease, lupus or myasthenia gravis, or will be in strong sun. Get prompt medical help for a severe headache with vision changes, or diarrhoea that is watery or bloody.

How we scored it

Dependence (98), track record (95) and overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (90) are strong. Serious side effects (82) reflect rare skin reactions, raised skull pressure and throat ulcers. Interactions (72) is the weakest factor because common minerals and antacids block absorption and isotretinoin should be avoided. Regulatory warnings (85) reflect a label without a boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary.