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An '''active ingredient''' is any [[ingredient]] that provides [[biological activity|biologically active]] or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure or any function of the body of humans or animals.<ref>{{Cite journal |author=Center for Drug Evaluation and Research |accessdate=2022-02-03 |title=Drugs@FDA Glossary of Terms |url=https://www.fda.gov/drugs/drug-approvals-and-databases/drugsfda-glossary-terms |journal=FDA |language=en |date=2017-11-14 }}</ref>
-The similar terms '''active pharmaceutical ingredient''' (abbreviated as '''API''') and '''bulk active''' are also used in medicine.<ref name="FTLOScience">{{cite web |url=https://ftloscience.com/drug-tablet-design/ |title=Drug Tablet Design: Why Pills Come in So Many Shapes and Sizes |date=2022-11-23 |first=Sean |last=Lim |accessdate=2023-03-05 |work=FTLOScience }}</ref> The term '''active substance''' may be used for [[natural product]]s.{{citation needed|date=March 2023}}
+The similar terms '''active pharmaceutical ingredient''' (abbreviated as '''API''') and '''bulk active''' are also used in medicine.<ref name="FTLOScience">{{cite web |url=https://ftloscience.com/drug-tablet-design/ |title=Drug Tablet Design: Why Pills Come in So Many Shapes and Sizes |date=2022-11-23 |first=Sean |last=Lim |accessdate=2023-03-05 |work=FTLOScience }}</ref><ref name="uscfr_2023_fdadrugdefinitions">{{cite web |title = § 207.1 What definitions and interpretations of terms apply to this part? |date = 2023-07-19 |work = US Code of Federal Regulations |url = https://www.ecfr.gov/on/2023-07-19/title-21/chapter-I/subchapter-C/part-207/subpart-A/section-207.1 |access-date = 2023-07-25 |publisher = US Government Publishing Office |archive-url = https://web.archive.org/web/20230725213043/https://www.ecfr.gov/on/current/title-21/chapter-I/subchapter-C/part-207/subpart-A/section-207.1 |archive-date = 2023-07-25 |url-status = live |quote = Active pharmaceutical ingredient means any substance that is intended for incorporation into a finished drug product and is intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the body. Active pharmaceutical ingredient does not include intermediates used in the synthesis of the substance. }}</ref> The term '''active substance''' may be used for [[natural product]]s.{{citation needed|date=March 2023}}
Some medication products can contain more than one active ingredient. The traditional word for the active pharmaceutical agent is '''pharmacon''' or '''pharmakon''' (from {{lang-el|φάρμακον}}, adapted from ''[[pharmacos]]'') which originally denoted a [[Potion|magical substance]] or drug.{{citation needed|date=March 2023}}