橫跨細胞膜的分子（通常是蛋白質），接受細胞外信號并傳導入細胞內。在藥理學里。受體更通常的是一個藥物靶分子。這樣的受體可以是蛋白質、酶、膜通道或外來病原體的一個區域。膜結合受體一般至少有兩到三個區域：一個接受信號的胞外區域，一個特征如水療法一樣沉浸其中的跨膜區域，一個傳導信號的胞質區域。藥物發現與識別受體結合分子與調節其行為有關。典型的識別分子或者象興奮劑，或者象抑制劑。抑制劑一般是小分子，他們不可逆轉地結合在受體上阻礙其正常功能，而興奮劑可以是小或大分子。當受體是酶時，藥物是典型的模仿自然發生的酶解物的分子，但它不可逆轉地結合在酶上，使其不能發揮作用。

A molecule (usually a protein) that spans a cell membrane and “receives” extracellular signals and transmits them into the cell. In pharmacology, a receptor is, more generically, any molecule that is a target for a drug. Thus a receptor may be a protein, enzyme, membrane channel, or a region of a foreign pathogen. Membrane-bound receptors typically have at least two or three domains: an extracellular domain that receives the signal; a membrane-spanning domain that is hydropathic in character (such as the 7-transmembrane alpha-helix domain structure found in many cellular receptors); and a cytoplasmic (effector) domain, that transmits the signal into the cell. Drug discovery is concerned with identifying molecules that bind to a receptor and modulate its behavior in some manner; typically the identifying molecule will behave as either an agonist (a molecule that stimulates the receptor) or as an antagonist (a molecule that inhibits the effect of the naturally occurring agonist of the receptor). Antagonists tend to be small molecules that bind irreversibly to the receptor preventing its normal function, while agonists may be small or large molecules (e.g. peptide or protein hormones). In the case where the receptor is an enzyme, the drugs are typically molecules that mimic the naturally occurring substrate of the enzyme, but that bind to it irreversibly so as to leave it in an inert, non-functional state (the “suicide” inhibitors).