Adrenocorticotropic hormone (ACTH) is a polypeptide hormone produced by the pituitary gland. Its principal function is stimulating the adrenal gland cortex to secrete a group of steroid hormones called glucocorticoids, which control the body's use of sugar and also help the body continue to function in stress situations. The first thirteen of ACTH's thirty nine amino acids are essential for production of the adrenal hormones. ACTH is prescribed medically to reduce inflammation and relieve pain.

The properties of ACTH were first investigated in the 1930s. In 1933, scientific groups headed by the Canadian biochemist James Collip, the American biologist Herbert Evans (1881-1971), and the Argentine physiologist Bernardo Houssay (1887-1971) used pituitary extracts to stimulate the adrenal cortex. The American biochemist Choh Hao Li was one of several scientists to isolate ACTH in 1943 and to synthesize it in 1963.

The American medical researchers Philip Hench and Edward Kendall studied the use of ACTH in treating arthritis. During World War II, Hench headed the first program to mass-produce ACTH for medical use. In 1948 and 1949, he and another colleague were the first to use it successfully in arthritic patients.

ACTH is now used to reduce inflammation in rheumatoid arthritis, ulcerative colitis, allergic reactions, and some types of hepatitis. It has also been tried in unproven treatment of multiple sclerosis. It is used diagnostically for diseases of the adrenal glands. ACTH levels in blood plasma decrease with age, and scientists are studying its use as an anti-aging drug. It is also currently being investigated in its ability to control seizures when injected in a gel form, although its mechanism of action is not known and it produces unfavorable side effects such as irritability, bloating, and decreased immune function.