<unk>  is readily absorbed from the gastrointestinal tract and freely crosses the blood–brain barrier. It acts primarily on the central nervous system (CNS), causing depression of the cough reflex, partly by a direct effect on the cough centre in the medulla. It is metabolized in the liver and its action may be prolonged in individuals with hepatic insufficiency (i.e. liver problems). Its use is therefore contraindicated in patients with liver disease, while care is advised in patients with hepatic impairment.
Pholcodine
Dextropropoxyphene
Chlormethine
Acetryptine
Maralixibat chloride
Acetomepregenol
Tiotixene
Methenmadinone acetate