Active ingredients are components in a drug which provide some pharmaceutical value, in contrast with the inactive ingredients, which act as carriers to make the drug easier for the body to process. The term “active ingredients” is also used in the pesticide industry to describe the active pesticides in a formulation. In both cases, these ingredients are literally “active,” performing a specific function upon application or ingestion.

Many drugs combine several active ingredients, and the interaction between these ingredients may be critical to the function of the drug. In synthetically compounded pharmaceuticals, manufacturers can tightly control the potency of their active ingredients, because they are formulated under controlled conditions. Herbalists and companies which use naturally sourced products must be careful with their formulations, because the potency of the active ingredients can vary widely, depending on factors which are out of the control of the manufacturer.

Brand name drugs rely on carefully patented and controlled active ingredients. Once patents expire and competitors can make generic versions, the generics typically use the same active ingredients, often in a formulation identical to that of the original drug. Sometimes, however, manufacturers make small changes which can have a profound impact on the effectiveness of the drug. For example, use of a different inactive ingredient might inadvertently change the potency of the drug, or the use of a different source for active ingredients could result in a drug with slightly different effects.

In the case of over the counter pharmaceuticals, the active ingredients are always listed on the back. It can be a good idea to compare active ingredients when considering which pharmaceutical to buy, as generic brands are often identical and much less expensive than store brands. Cough syrup, for example, might be priced radically differently depending on the manufacturer, but the active ingredients will be the same. Comparing pharmaceuticals before purchase can save money for savvy shoppers.

Inactive ingredients, also known as excipients, can perform a number of functions. For example, some active ingredients cannot be absorbed very well by the body, so they must be combined with a soluble excipient so that the body can process them. In other cases, active ingredients are very strong, and combining them with an excipient allows greater control over the dosage; without an excipient, a powerful pill might be the size of a pinhead, but with an excipient, it can be formulated into a larger and manageable size.