Minocycline hydrochloride, also known as minocycline, is a broad spectrum tetracycline antibiotic, and has a broader spectrum than the other members of the group. It is a bacteriostatic antibiotic, classified as a long-acting type. As a result of its long half-life it generally has serum levels 2-4 times that of most other tetracyclines (150 mg giving 16 times the activity levels compared to 250 mg of tetracycline at 24–48 hours). Minocycline was originally discovered by Lederle Laboratories and marketed under the brand name Minocin.

It is primarily used to treat acne and other skin infections as well as lyme disease as the one pill twice daily 100 mg dosage is far easier for patients than the four times a day required with tetracycline or oxytetracycline.

Although minocycline's broader spectrum of activity, compared to other members of the group, includes activity against Neisseria meningitidis, its use as a prophylaxis is no longer recommended because of side effects (dizziness and vertigo).

It may be used to treat certain strains of MRSA infection and disease caused by drug resistant Acinetobacter.

Minocycline is recognized as a DMARD (Disease-Modifying Anti-Rheumatic Drug) by the American College of Rheumatology, which recommends its use as a treatment for mild rheumatoid arthritis.

For other uses of minocycline see tetracycline antibiotics and oxytetracycline as the uses are much the same between tetracyclines with only minor exceptions.

Contrary to most other tetracycline antibiotics (doxycycline excluded), minocycline may be used in renal impairment, but may aggravate systemic lupus erythematosus. It may also trigger or unmask autoimmune hepatitis.

Also, more so than other tetracyclines, minocycline can cause the rare condition of secondary intracranial hypertension which has initial symptoms of headache, visual disturbances, dizziness, vomiting, and confusion. Cerebral edema, as well as autoimmune rheumatoid arthritis are rare side effects to minocycline in some people.

Minocycline, like all tetracyclines, becomes dangerous past its expiration date. While most prescription drugs lose potency after their expiration dates, tetracyclines were known to become toxic over time due to the breakdown of certain chemicals present in the manufactured capsules. This is not a present concern in drugs manufactured in developed countries. Expired tetracyclines, as previously manufactured, can cause serious damage to the kidneys.

Minocycline's absorption is impaired if taken at the same time of day as calcium or iron supplements. Unlike some of the other tetracycline group antibiotics, it can be taken with calcium-rich foods such as milk, although this does reduce the absorption slightly. Should be taken with plenty of water. If taking this drug, one should avoid prolonged or excessive exposure to direct sunlight. A study published in 2007 mentioned that Minocycline harms ALS patients. Patients on minocycline declined more rapidly than those on placebo. At present the mechanism of this side effect is unknown. According to the researcher from Columbia University the effect does not seem to be dose dependent because the patients on high doses did not do worse than those on the low doses..