The hydrochloride salt of alfentanil, a synthetic short-acting opioid with analgesic and local anesthesia enhancing activity. Alfentanil hydrochloride primarily binds to mu-opioid receptor, a G-protein-coupled receptor, thereby mimicking the actions of morphine, the prototypical mu receptor agonist. This agent induces anti-nociception responses mediated through inhibiting the release of various neurotransmitters such as substance P, GABA, dopamine, acetylcholine and noradrenaline; in addition, the release of vasopressin, somatostatin, insulin and glucagon are also inhibited.