Niaprazine (Nopron) is a sedative–hypnotic drug of the phenylpiperazine class.^[1] It has been used in the treatment of sleep disturbances since the early 1970s in several European countries, including France, Italy, and Luxembourg.^[2][3] It is commonly used with children and adolescents on account of its favorable safety and tolerability profile and lack of abuse potential.^{[4][5][6][7][8][9]}

Originally believed to act as an antihistamine and anticholinergic,^[10] niaprazine was later discovered to have no significant binding affinity for either the H₁ or the mACh receptors (K_i = > 1 μM), and was instead found to act as a potent and selective 5-HT_2A and α₁-adrenergic receptor antagonist (K_i = 75 nM and 86 nM, respectively).^[11] It is virtually inactive at 5-HT_1A, 5-HT_2B, D₂, and β-adrenergic, as well as at SERT and VMAT (K_i = all > 1 μM), but it does have some weak affinity for the α₂-adrenergic receptor (K_i = 730 nM),^[11] likely acting as an antagonist there as well.

Niaprazine has been shown to metabolize to the compound pFPP in a similar manner to how trazodone and nefazodone metabolize to mCPP.^[12][13] It is unclear what role, if any, pFPP plays in the clinical effects of niaprazine.^[11] However, from animal studies it is known that pFPP, unlike niaprazine, does not produce sedative effects, and instead exerts a behavioral profile indicative of serotonergic activation.^[12]