Cyproheptadine hydrochloride is an antagonist of serotonin receptor [1].
Cyproheptadine is a serotonin and histamine antagonist as well as an antimuscarinic reagent. It is used to treat for postgastrectomy-dumping syndrome, pruritic dermatoses, migraine, anorexia, and pituitary-dependent Cushing's syndrome. The major urinary product of cyproheptadine is cyproheptadine glucuronide, a quaternary ammonium compound. Cyproheptadine has some side effects including sedation, drowsiness, hypotension, tachycardia and blood dyscrasias. As a 5-HT2A receptor antagonist, cyproheptadine is found to reverse serotonin-enhanced ADP-induced platelet aggregation in vitro and ex vivo suggesting its antiplatelet and thromboprotective effects. [1, 2]
References:
[1] Levine B, Green-Johnson D, Hogan S, Smialek JE. A cyproheptadine fatality. J Anal Toxicol. 1998 Jan-Feb;22(1):72-4.
[2] Lin OA, Karim ZA, Vemana HP, Espinosa EV, Khasawneh FT. The antidepressant 5-HT2A receptor antagonists pizotifen and cyproheptadine inhibit serotonin-enhanced platelet function. PLoS One. 2014 Jan 23;9(1):e87026.