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What is Doxycycline?
Doxycycline is a tetracycline antibiotic used to treat a wide range of bacterial infections, including respiratory tract infections, urinary tract infections, sexually transmitted infections like chlamydia, certain skin infections, and tick borne diseases such as Lyme disease. It is also prescribed for the treatment and prevention of malaria in certain regions, and for managing acne.
It is available in strengths of 50 mg, 75 mg, 100 mg, and 150 mg as capsules, tablets, or suspension. Doxycycline will not treat viral infections like colds or the flu. Because generic doxycycline is widely available, many people compare pharmacy prices for cheap refills or buy it online from licensed U.S. pharmacies, ensuring clear labeling, correct strength, and a valid expiration date.
How It Works
Doxycycline works by inhibiting bacterial protein synthesis. It binds to the 30S ribosomal subunit in bacteria, blocking the production of proteins necessary for growth and replication. This stops the spread of the infection, allowing the immune system to clear the bacteria.
Doxycycline is well absorbed from the gut and widely distributed throughout the body, making it effective for infections in many tissues, including the lungs, skin, and urinary tract.
What you may notice
Fever, swelling, or pain from the infection may improve within a few days, but it is important to complete the prescribed course even if symptoms resolve early.
Dosage Information
The dose and duration depend on the infection type, severity, and patient factors such as age and kidney function. Always follow your clinician’s directions.
- Most bacterial infections in adults: 100 mg twice on the first day, then 100 mg once or twice daily.
- Acne: 50 mg to 100 mg once daily.
- Lyme disease: 100 mg twice daily for 10 to 21 days.
- Malaria prevention: 100 mg once daily starting 1 to 2 days before travel, during travel, and for 4 weeks after leaving the area.
How to take it
Take doxycycline with a full glass of water and remain upright for at least 30 minutes to reduce the risk of esophageal irritation. It may be taken with food if stomach upset occurs, but avoid dairy products close to the dose, as calcium can reduce absorption. If you miss a dose, take it when remembered unless it is almost time for your next scheduled dose—then skip it. Do not double up.
Cost and access tips
Generic doxycycline is inexpensive and widely available. Buying from licensed online pharmacies can save money. Cheap pricing is fine when labeling and expiration dates are clear, and a pharmacist is available for consultation.
Side Effects
Common side effects include nausea, diarrhea, stomach upset, and increased sensitivity to sunlight. Use sunscreen and avoid tanning beds during treatment.
Less common but important
- Esophageal irritation or ulcers: More likely if taken without enough water or before lying down.
- Severe allergic reaction: Rash, swelling, or trouble breathing require immediate medical attention.
- Intracranial hypertension: Rare but possible; symptoms include headache and vision changes.
- Liver problems: Rare but serious; report yellowing of the skin or eyes.
Warnings & Interactions
Doxycycline should not be used in children under 8 years of age unless necessary, as it can cause permanent tooth discoloration. It should also be avoided during pregnancy unless the benefits outweigh the risks. Use with caution in people with liver disease.
Drug interactions
- Antacids, iron, calcium, and magnesium supplements: Can reduce absorption; separate by at least 2 hours.
- Blood thinners: Doxycycline can increase the effect of warfarin, requiring closer monitoring.
- Other antibiotics: May interfere with bactericidal antibiotics like penicillin.
Practical safety tips
Complete the full course even if you feel better. Avoid prolonged sun exposure. If buying doxycycline online, use licensed U.S. pharmacies, verify the strength and expiration date, and ensure labeling is clear. Cheap pricing is acceptable when those checks are met.
Frequently Asked Questions
Many people notice improvement in symptoms within a couple of days, but you should complete the full prescribed course to fully clear the infection.
It's best to avoid taking it with milk or dairy products alone, as calcium can reduce absorption. You can have dairy at other times of the day.
No. It only works against bacterial infections and will not help with colds, flu, or other viral illnesses.
Take it when remembered unless it is almost time for your next dose. If so, skip the missed dose. Do not double up.
Yes. It increases sun sensitivity, so wear sunscreen and protective clothing when outdoors.
It is generally avoided during pregnancy due to potential effects on the baby's teeth and bones, unless your doctor decides it's necessary.
Moderate alcohol use is unlikely to affect doxycycline, but alcohol can slow your recovery from infection.
Yes, if purchased from a licensed U.S. pharmacy with clear labeling and expiration dates. Cheap pricing is fine when those checks are met.
Most evidence suggests it does not reduce birth control pill effectiveness, but use a backup method if you have severe vomiting or diarrhea.
Yes. It can reduce inflammation and bacteria in the skin. Acne treatment often lasts several weeks to months for best results.
Medical Disclaimer
This website provides informational overviews of medications and does not offer medical advice, diagnosis, or treatment. Always consult a licensed healthcare provider before starting or changing any medication.
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This page was last medically reviewed: August 2025
Educational information only. Doxycycline should be used under clinician supervision. Not for viral infections. Complete the full course to prevent resistance.