There is no difference between doxycycline and doxycycline hydrochloride, both belong to a class of drugs, which are tetracycline antibiotics. Doxycycline can treat rickettsial disease, Mycoplasma spp. infections, regression fever, cholera, rabbit fever, and Lyme disease; it is used for sensitive Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, and other infections; and it can be applied to patients with allergy to penicillin antibiotics, such as tetanus, gas gangrene, and so on. Doxycycline is prohibited for those who have a history of allergy to doxycycline and those who have a history of allergy to any variety of tetracycline, and should be avoided in pregnancy, lactation and children under 8 years of age. Adverse reactions such as enamel hypoplasia, dental caries, nausea, vomiting, abdominal distension, diarrhea, epigastric discomfort, dry mouth, and sore throat may occur after doxycycline application. Before taking doxycycline, you should consult a medical professional and take it under the guidance of a doctor.