(3S,11bS)-Tetrabenazine-[d6], is the labelled analogue of (3S,11bS)-Tetrabenazine. (3S,11bS)-Tetrabenazine is one of Tetrabenazine impurities. Tetrabenazine is a VMAT-inhibitor used for treatment of hyperkinetic movement disorder. It is a monoamine-depleting and a dopamine-receptor-blocking drug and is an effective and safe drug for the treatment of a variety of hyperkinetic movement disorders.