Baclofen (brand names Kemstro and Lioresal) is a derivative of gamma-aminobutyric acid (GABA) primarily used to treat spasticity.

It is an agonist specific to mammalian but not fruit fly (Drosophila) GABAB receptors.[1][2] Its beneficial effects result from actions at spinal and supraspinal sites. Baclofen can also be used to treat hiccups. It has been shown to prevent rises in body temperature induced by the drug MDMA in rats. [3] A very beneficial property of baclofen is that tolerance does not seem to occur to any significant degree - baclofen retains its therapeutic anti-spasmodic effects even after many years of continued use.[4] However, oral dosage must be carefully regulated; significantly high doses of the drug, particularly 80 milligrams per day or higher, can cause excessive drowsiness that can interfere with daily function.

Can also be used to treat addiction in some cases.