Aromatic-L-amino-acid decarboxylase (, synonyms: DOPA decarboxylase, tryptophan decarboxylase, 5-hydroxytryptophan decarboxylase, AAAD) is an enzyme catalyzing the decarboxylation of L-DOPA or 5-HTP to yield the neurotransmitters dopamine and serotonin (5-HT), respectively. The enzyme uses pyridoxal phosphate as a cofactor. In normal dopamine and 5-HT neurotransmitter synthesis, AAAD is not the rate-limiting step of in either reaction. However, AAAD becomes the rate-limiting step of dopamine formation in Parkinson's Disease patients treated with L-DOPA.

AAAD is the rate-limiting enzyme in the formation of biogenic trace amines.

The same enzyme is also able to the decarboxylate the amino acid tryptophan to tryptamine, a precursor to many alkaloids found in plants and animals.

EC 4.1.1