Doxycycline: what it treats, how to take it, side effects
Last updated September 3, 2026.
Doxycycline is a tetracycline antibiotic used for bacterial infections, acne, rosacea, and malaria prevention. It stops bacteria from growing and spreading. Like every antibiotic, it does not work on colds, flu, or other viruses.
What does it treat?
Doxycycline treats infections caused by bacteria, including infections spread by ticks, lice, mites, and infected animals. It is also prescribed for acne (it kills pore-infecting bacteria and lowers skin oil), for rosacea (it decreases inflammation), and to prevent malaria in travelers. MedlinePlus also notes its use for Lyme disease in certain tick-bite situations and, in certain circumstances, to prevent some sexually transmitted infections.
How do you take it?
The label's usual adult regimen is 200 mg on the first day (100 mg every 12 hours), then 100 mg once daily; more severe infections may stay at 100 mg every 12 hours. Take each dose with a full glass of water, and if it upsets your stomach, take it with food or milk. Swallow delayed-release tablets whole. Timing matters with other products: antacids, calcium supplements, and magnesium-containing laxatives go 1 to 2 hours before or after doxycycline, and iron products go 3 hours before or 2 hours after. For malaria prevention, start 1 to 2 days before entering the malaria area, take it daily while there, and continue for 4 weeks after leaving - and still use repellent, nets, and covered clothing, because the drug is not full protection. Finish the whole course, and never double a missed dose.
Side effects to know
- Common: nausea, vomiting, diarrhea, loss of appetite, rectal or vaginal itching or irritation, vaginal discharge, sore throat, swollen tongue, dry mouth, anxiety, back pain, and changes in the color of skin, scars, nails, or the mouth.
- Serious: headache with blurred or double vision or vision loss (a pressure problem in the skull); rash with fever or swollen glands; blistering or peeling skin; unusual bleeding or bruising; watery or bloody stools with cramps or fever, even months after stopping; and allergic reactions with swelling or trouble breathing. Call your doctor immediately for these.
Who should not take it?
Doxycycline can harm a fetus - if you are pregnant or become pregnant while taking it, call your doctor immediately - and your doctor may tell you not to breastfeed during treatment. It permanently stains developing teeth and can affect bone growth, so it is not used in children under 8 except for specific serious infections like inhalational anthrax or Rocky Mountain spotted fever. It can also reduce the effectiveness of hormonal birth control, so use a backup method. Flag for your doctor: lupus, intracranial hypertension, yeast infections, stomach surgery, asthma, kidney or liver disease, and current diarrhea. MedlinePlus flags interactions with bismuth, omeprazole, and lansoprazole. Expect sun sensitivity - protective clothing and sunscreen are part of the treatment.
When is it an emergency?
Call 911 for an allergic reaction with swelling of the eyes, face, throat, tongue, or lips, or difficulty breathing or swallowing. A severe headache with blurred or double vision, a blistering or peeling rash, or watery or bloody diarrhea with cramps or fever means calling your doctor immediately. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why do I need sunscreen on doxycycline?
Doxycycline makes skin sensitive to sunlight, and MedlinePlus advises planning ahead: avoid unnecessary or prolonged sun exposure and wear protective clothing, sunglasses, and sunscreen. Ordinary midday sun can cause a burn that looks and feels worse than usual.
Can I take doxycycline with milk or food?
Yes - MedlinePlus says if your stomach gets upset, you can take doxycycline with food or milk. The stricter spacing rules belong to antacids, calcium supplements, and magnesium laxatives (1 to 2 hours apart) and iron products (3 hours before or 2 hours after), which interfere with absorption.
Why do I have to drink a full glass of water with it?
MedlinePlus instructs a full glass of water with each dose. Washing the pill down well helps it reach the stomach instead of sitting in the esophagus, where it can irritate - a practical step worth taking seriously.
How does doxycycline prevent malaria?
Taken daily, it suppresses the malaria parasite. The schedule from MedlinePlus: start 1 to 2 days before travel to the malaria area, continue every day while there, and keep taking it for 4 weeks after leaving, for no more than 4 months total. It is not full protection on its own - use insect repellent, bed nets, and covered clothing too.
Does doxycycline affect birth control?
It can. MedlinePlus says doxycycline may decrease the effectiveness of hormonal contraceptives (pills, patches, rings, injections), so use another method of contraception while taking it and talk to your doctor about backup options.
Can I drink alcohol while taking doxycycline?
Neither the FDA label nor MedlinePlus lists a specific alcohol interaction for doxycycline. That said, alcohol can aggravate stomach upset and dehydration during an infection, so many clinicians suggest avoiding it during the course - ask your doctor for guidance on your situation.