Molecules that activate (or, in some cases, inhibit) receptors can be classified as hormones, neurotransmitters, cytokines, and growth factors, but all of these are called receptor ligands.

The genes and receptor ligands are as follows:

Apolipoproteins also serve as enzyme cofactors, receptor ligands, and lipid transfer carriers that regulate the metabolism of lipoproteins and their uptake in tissues.

Other synthetic nuclear receptor ligands have no apparent effect on gene transcription in the absence of endogenous ligand.

NS102 is a kainate receptor ligand.

Salvinorin A is not an alkaloid, (meaning it does not contain a basic nitrogen), unlike most known opioid receptor ligands.

NE-100 was one of the earliest selective sigma-1 receptor ligands reported and has been widely used as a pharmacological tool.

Kisspeptin is a G-protein coupled receptor ligand for GPR54.

When activated by Toll-like receptor ligands, the CD80 expression is upregulated in antigen presenting cells (APCs).

Fluo-4 is used to measure calcium (Ca) concentrations inside living cells, and is often used for high-throughput screening of receptor ligands and calcium permeable ion channels.