Doxycycline is used to treat syphilis. Syphilis is a sexually transmitted disease caused by syphilis spirochete infection, in the treatment of syphilis, doxycycline belongs to the second choice of drugs, but compared to penicillin, its half-life, efficacy and other aspects will be relatively inferior. Doxycycline belongs to the tetracycline class of antibiotics, can be used for the treatment of syphilis, clinically the first choice for syphilis treatment is benzylpenicillin, usually in the case of penicillin allergy, you can choose other types of sensitive antibiotics. For example, cephalosporin and tetracycline antibiotics. The use of doxycycline for the treatment of syphilis, need to be prescribed under the treatment of a professional physician, not self-blind medication, so as not to delay the condition.