(+)-alpha-Dihydrotetrabenazine (HTBZ) is an active component of tetrabenazine. Tetrabenazine is a mixture of closely-related compounds (isomers) and is readily metabolized in the human body to HTBZ and related isomers. Tetrabenazine is a drug for the symptomatic treatment of hyperkinetic movement disorder and is marketed under the trade names Nitoman in Canada and Xenazine in New Zealand and some parts of Europe, and is also available in the USA as an orphan drug. (+)-alpha-Dihydrotetrabenazine and related benzo[a]quinolizines have been labeled with tritium and carbon-11 radioisotopes and used for in vitro and in vivo studies of the VMAT2 in animal and human brain. Adeptio Pharmaceuticals is developing alpha-dihydrotetrabenazine (HTBZ) for the treatment of neurological disorders. It acts by inhibiting vesicular monoamine transporter 2 (VMAT2), thereby blocking the transport of dopamine into axon terminals or into storage vesicles.