An international nonproprietary name (INN) is an official generic and nonproprietary name given to a pharmaceutical substance or an active ingredient, encompassing compounds, peptides and low-molecular-weight proteins (e.g., insulin, hormones, cytokines), as well as complex biological products, such as those used for gene therapy. INNs are intended to make communication more precise by providing a unique standard name for each active ingredient, to avoid prescribing errors. The INN system was initiated by the World Health Organization (WHO) in 1953.
Having unambiguous standard names for each pharmaceutical substance (standardization of drug nomenclature) is important because a drug may be sold under many different brand names, or a branded medication may contain more than one drug. For example, the branded medications Celexa, Celapram and Citrol all contain the same active ingredient whose INN is citalopram. The antibacterial medication known as co-trimoxazole as well as those under the brand names Bactrim and Septran all contain two active ingredients easily recognisable by their INN: trimethoprim and sulfamethoxazole.