Tetracycline is a broad-spectrum antibiotic. It is effective against a wide variety of bacteria including Hemophilus influenzae, Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydia psittaci, Chlamydia trachomatis, Neisseria gonorrhoeae, and many others. Chlortetracycline, the first drug of the tetracycline family, was introduced in 1948.

For most infections, tetracycline is taken two to four times daily for 7 to 14 days. It should be taken at least one hour before or two hours after meals to prevent binding to food and result in reduced absorption of the tetracycline.
Capsules should be kept below 30°C (86°F).

Most common side effects are diarrhea or loose stools, nausea, abdominal pain, and vomiting. Tetracycline is generally well-tolerated. It may cause discoloration of teeth if used in patients below 8 years of age. Exaggerated sunburn can occur with tetracyclines; therefore, sunlight should be minimized during treatment.

It is recommended that tetracycline not be taken at the same time as aluminum-, magnesium-, or calcium- based antacids, such as Mylanta, Maalox, Tums, or Rolaids since, like food, these compounds bind tetracycline in the intestine. Similarly, tetracycline should not be taken with minerals (such as calcium or iron), with bismuth subsalicylate (Pepto-Bismol) or with dairy products.
Tetracycline may enhance the activity of warfarin (Coumadin) and result in excessive "thinning" of the blood, necessitating a reduction in the dose of warfarin. Phenytoin (Dilantin), carbamazepine (Tegretol), and barbiturates (such as phenobarbital) can enhance the metabolism of tetracycline.

Tetracycline is used for various infections including respiratory tract infections due to Hemophilus influenzae, Streptococcus pneumoniae, or Mycoplasma pneumoniae. It is also used for nongonococcal urethritis (due to Ureaplasma), Rocky Mountain spotted fever, typhus, chancroid, cholera, brucellosis, anthrax, syphilis, and acne. It is used in combination with other medications to treat Helicobacter pylori, the bacteria associated with ulcers of the stomach and duodenum.