Wiktionary
n. The specific compound in a natural or man-made mixture that is responsible for the mixture's activity.
Wikipedia
An active ingredient (AI) is the ingredient in a pharmaceutical drug that is biologically active. The similar terms active pharmaceutical ingredient (API) and bulk active are also used in medicine, and the term active substance may be used for natural products. Some medication products may contain more than one active ingredient. The traditional word for the API is pharmacon or pharmakon (from , adapted from pharmacos) which originally denoted a magical substance or drug.
The term active constituent is often chosen when referring to the active substance of interest in a plant (such as salicylic acid in willow bark or arecoline in areca nuts), because the word ingredient in many minds connotes a sense of human agency (that is, something that a person combines with other substances), whereas the natural products present in plants were not added by any human agency but rather occurred naturally ("a plant doesn't have ingredients").
In contrast with the active ingredients, the inactive ingredients are usually called excipients in pharmaceutical contexts. The main excipient that serves as a medium for conveying the active ingredient is usually called the vehicle. Petrolatum and mineral oil are common vehicles.
Usage examples of "active ingredient".
In former days, Box was the active ingredient in a once-famous remedy for the bite of a mad dog.
Listen, doofus, what do you suppose is the active ingredient in Roach Prufe?
THC is the primary psycho- active ingredient which is acted upon synergistically by small amounts of CBN, CBD, and other accessory cannabi- noids.
At the very least, we could obtain a source of the active ingredient in the cornerstone of your drug empire that would allow you to manufacture safe batches for a long, long time.
I recalled vaguely from a long-ago botany lecture hearing that willow bark in fact contained salicylic acid, the active ingredient in aspirin.
The active ingredient contained forty-six molecules, including a slight molecular variation of a steroid, fluoxymesterone, a hormonelike compound which Chris had never seen in a plant beforewhat he named tabulone.
John Wilkes gallantly kissed the hand of Julia, as though they had just met, and simultaneously slipped her a packet of chloral hydrate crystals, which would be the active ingredient in a Mickey Finn for the chaperone.
But there does seem to be a treatment and we know the active ingredient.
You then add the precise quantity by weight of the active ingredient, in my case cantharidin powder.
The active ingredient is mescaline, which is supposed to induce religious visions.
But she was dead, unaware that the active ingredient which soothed her heartburn was a chemical derivative of belladonna, known quaintly in some European countries as the hand of glory.