active ingredient
Technical term used in pharmacology and related fields to refer to the component of a drug or product that produces the intended effect.
The active ingredient in this medicine is acetaminophen.
Please check the active ingredients in the cosmetic product.
成分 is a general term for 'ingredient' or 'component', while 有効成分 specifically refers to the active or effective ingredient in a product.
Compound of 有効 (effective) and 成分 (ingredient). The exact historical derivation is uncertain, but the term is a straightforward modern technical coinage.