A Decarboxylation is any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as carbon dioxide (CO₂).

Common biosynthetic decarboxylations of amino acids to amines are:

tryptophan to tryptamine, phenylalanine to phenylethylamine, tyrosine to tyramine, histidine to histamine, serine to ethanolamine, glutamic acid to GABA, lysine to cadaverine, arginine to agmatine, ornithine to putrescine, 5-HTP to serotonin, and L-DOPA to dopamine.

Other decarboxylation reactions from the citric acid cycle include:

pyruvate to acetyl-CoA, oxalosuccinate to α-ketoglutarate, and α-ketoglutarate to succinyl-CoA.

Enzymes that catalyze decarboxylations are called decarboxylases or, more formally, carboxy-lyases (E.C.4.1.1).

Chemical decarboxylations reactions often require extensive heating in high-boiling solvents. Copper salts are often added as catalysts. Also the addition of catalytic amounts of cyclohexen-2-one has been reported to catalyze the decarboxylation of amino acids. Decarboxylations are especially easy for alpha-keto acids due to the formation of a cyclic transitional state.