Doxycycline is a broad-spectrum antibiotic used to treat a wide range of bacterial infections, from acne and respiratory infections to sexually transmitted infections, Lyme disease, and malaria prevention. It belongs to the tetracycline family and has been a staple in clinical practice for over four decades, largely because it works against so many different types of bacteria while remaining affordable and easy to take by mouth.
How Doxycycline Works
Doxycycline stops bacteria from growing by blocking their ability to make proteins. It latches onto a key part of the bacterial ribosome (the cell’s protein-building machinery), which prevents the bacterium from assembling the proteins it needs to survive and multiply. This makes it bacteriostatic, meaning it halts bacterial growth rather than directly killing bacteria, giving your immune system time to clear the infection.
Respiratory and Sinus Infections
Doxycycline is commonly prescribed for respiratory tract infections, including certain types of pneumonia, bronchitis, and sinus infections. It’s particularly effective against a type of bacteria called walking pneumonia, which causes a milder but persistent form of pneumonia. It’s also used for upper respiratory infections when other antibiotics aren’t appropriate. For most respiratory infections, treatment courses are relatively short, often 7 to 14 days.
Acne and Rosacea
For moderate to severe inflammatory acne, doxycycline is one of the most frequently prescribed oral antibiotics. It reduces the bacteria that contribute to breakouts and has anti-inflammatory properties that help calm red, swollen lesions. Treatment courses for acne typically last several weeks to a few months.
Rosacea, which causes facial redness and pimple-like bumps, is treated with a lower dose of doxycycline (40 mg once daily). At this dose, the drug works primarily as an anti-inflammatory rather than an antibiotic, which means it can be used for longer periods without the same concerns about antibiotic resistance.
Sexually Transmitted Infections
Doxycycline is a first-line treatment for several STIs. Chlamydia infections of the urethra, cervix, or rectum are commonly treated with it. It’s also used for nongonococcal urethritis and lymphogranuloma venereum, both caused by sexually transmitted bacteria. When someone is allergic to penicillin, doxycycline serves as an alternative for treating syphilis and gonorrhea.
In 2024, the CDC issued new guidelines for using doxycycline as post-exposure prophylaxis (doxy-PEP) to prevent bacterial STIs. Under these guidelines, men who have sex with men and transgender women who’ve had a bacterial STI in the past 12 months can take a 200 mg dose within 72 hours after sex to reduce their risk of contracting syphilis, chlamydia, or gonorrhea. This use requires ongoing follow-up and STI testing every 3 to 6 months.
Tick-Borne Diseases and Lyme Disease
Doxycycline is the go-to antibiotic for tick-borne illnesses. It’s the recommended treatment for Rocky Mountain spotted fever, typhus, ehrlichiosis, and anaplasmosis. For these rickettsial diseases, starting treatment quickly is critical, and doctors are advised not to wait for test results before prescribing.
For Lyme disease, most cases respond to 10 to 14 days of antibiotics, with doxycycline being one of the primary choices. In some situations, a single dose of doxycycline taken shortly after a tick bite in an area where Lyme disease is common can lower the risk of developing the infection in the first place.
Malaria Prevention for Travelers
If you’re traveling to an area where malaria is common, doxycycline is one of the options for preventive treatment. You start taking 100 mg once daily 1 to 2 days before entering the malaria-endemic area, continue through your trip, and keep taking it for 4 weeks after you leave. It’s often the most affordable option compared to other antimalarial drugs, though the 4-week tail after travel is longer than some alternatives require.
Anthrax Exposure
Doxycycline is approved for preventing and treating anthrax, including inhalational anthrax after a known or suspected exposure. The protocol calls for 100 mg twice daily, taken 12 hours apart, for up to 60 days depending on the exposure. This is primarily relevant in bioterrorism scenarios or occupational exposures. Adults and children weighing 76 pounds or more take the same standard dose.
Other Approved Uses
The list of infections doxycycline can treat is unusually long for a single antibiotic. Beyond the common uses above, it’s approved for:
- Cholera
- Plague
- Tularemia (rabbit fever)
- Brucellosis (used alongside another antibiotic)
- Psittacosis (parrot fever, contracted from birds)
- Certain eye infections caused by chlamydia, including trachoma and inclusion conjunctivitis
Many of these are uncommon in developed countries, but doxycycline remains an essential tool for treating them when they do occur.
Sun Sensitivity and Other Side Effects
The most notable side effect of doxycycline is photosensitivity. While taking it, your skin becomes significantly more prone to sunburn, even with brief sun exposure. This reaction is dose-related, so higher doses carry greater risk. It typically causes a painful, sunburn-like rash on exposed skin, and in rare cases can lead to blistering or nail changes. Wearing sunscreen and protective clothing during treatment isn’t optional; it’s essential.
Gastrointestinal side effects are also common. Nausea, stomach upset, and diarrhea affect a meaningful number of people. One specific risk worth knowing about: doxycycline can cause ulceration of the esophagus if it gets stuck on its way down. To prevent this, take it with a full glass of water or with a meal, and stay upright (sitting or standing) for at least 30 minutes afterward. Unlike many antibiotics, doxycycline can be taken with food without significantly reducing absorption, so eating with your dose is actually the safest approach.
Use in Children
Older antibiotics in the tetracycline family are known to stain permanent teeth when given to children under 8. Doxycycline, however, binds less readily to calcium and has not been shown to cause the same staining. The largest studies to date found no dental staining in children under 8 who received short courses of doxycycline. Both the American Academy of Pediatrics and the CDC recommend doxycycline for children of all ages when treating suspected tick-borne diseases, emphasizing that concerns about tooth discoloration should not delay treatment for potentially life-threatening infections.