Doxycycline is an antibiotic medication used to treat a wide variety of bacterial infections, including respiratory tract infections, urinary tract infections, and acne. It may also be used to treat malaria and Lyme disease, or to prevent Lyme disease in certain people who have been bitten by a tick. The active ingredient in doxycycline is doxycycline hyclate, which corresponds to 100mg doxycycline per capsule. In addition to the active ingredient, doxycycline capsules contain inactive ingredients such as colloidal silicon dioxide, magnesium stearate, and microcrystalline cellulose. The capsule shell may also contain other ingredients such as gelatin, titanium dioxide, and iron oxide. Doxycycline may cause side effects, and patients should talk to their doctor about any possible risks before taking the medication.