横跨细胞膜的分子（通常是蛋白质），接受细胞外信号并传导入细胞内。在药理学里。受体更通常的是一个药物靶分子。这样的受体可以是蛋白质、酶、膜通道或外来病原体的一个区域。膜结合受体一般至少有两到三个区域：一个接受信号的胞外区域，一个特征如水疗法一样沉浸其中的跨膜区域，一个传导信号的胞质区域。药物发现与识别受体结合分子与调节其行为有关。典型的识别分子或者象兴奋剂，或者象抑制剂。抑制剂一般是小分子，他们不可逆转地结合在受体上阻碍其正常功能，而兴奋剂可以是小或大分子。当受体是酶时，药物是典型的模仿自然发生的酶解物的分子，但它不可逆转地结合在酶上，使其不能发挥作用。

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).