Doxycycline is a broad-spectrum antibiotic of the tetracycline class used in the treatment of infections caused by bacteria and certain parasites. It is used to treat bacterial pneumonia, acne, chlamydia infections, Lyme disease, cholera, typhus, and syphilis. It is also used to prevent malaria.
Doxycycline may be taken by mouth or by injection into a vein.
Common side effects include diarrhea, nausea, vomiting, abdominal pain, and an increased risk of sunburn. Use during pregnancy is not recommended.
 Like other agents of the tetracycline class, it either slows or kills bacteria by inhibiting protein production. It kills malaria by targeting a plastid organelle, the apicoplast.
 
Specifically, doxycycline is indicated for treatment of the following diseases:
Rocky Mountain spotted fever, typhus fever and the typhus group, scrub typhus, Q fever, rickettsialpox, and tick fevers caused by Rickettsia,
respiratory tract infections caused by Mycoplasma pneumoniae,
Lymphogranuloma venereum, trachoma, inclusion conjunctivitis, and uncomplicated urethral, endocervical, or rectal infections in adults caused by Chlamydia trachomatis,
psittacosis,
non-gonococcal urethritis caused by Ureaplasma urealyticum,
relapsing fever due to Borrelia recurrentis,
chancroid caused by Haemophilus ducreyi,
plague due to Yersinia pestis,
tularemia,
cholera,
campylobacter fetus infections,
brucellosis caused by Brucella species (in conjunction with streptomycin),
bartonellosis,
granuloma inguinale (Klebsiella species),
Lyme disease (Borrelia species).