Partial Agonist
Definition
An agonist that cannot produce the full response however much of it is present, because it activates the receptor less completely than the natural ligand does. Against a full agonist it can behave as a brake.
What this means for research sourcing
Mechanistic terms like this describe how research compounds behave in vitro. See the mechanism overviews for compounds Volta stocks.
Related Terms in Pharmacology
Dual Agonist
One molecule that activates two receptors. Tirzepatide is a GLP-1 and GIP agonist; survodutide combines GLP-1 with glucagon-receptor activity. The pairing is a design decision about which pathways to engage at once.
Triple Agonist
One molecule that activates three receptors. Retatrutide acts at the GLP-1, GIP and glucagon receptors, and it is the compound that put the class into clinical development.
Binding Affinity
How tightly a molecule holds its receptor, reported as a dissociation constant where a lower number means tighter binding. Affinity alone does not predict the size of a response: that also depends on how well the bound molecule activates the receptor.
EC50
The concentration producing half of a compound's maximum effect in a given assay. It is a potency measure and is only comparable between compounds tested in the same system, which is why cross-paper EC50 comparisons mislead so often.
Potency
How little of a compound is needed to produce a given effect. A more potent molecule works at a lower concentration, which says nothing about whether its maximum achievable effect is larger.
Receptor Selectivity
How far a compound acts on its intended receptor rather than on related ones. Selectivity is the difference between a GHRP that raises growth hormone alone and one that also moves cortisol and prolactin.
Desensitization
A fall in receptor responsiveness under prolonged or repeated stimulation, achieved by internalising receptors or expressing fewer of them. It is one mechanism behind an effect that fades while exposure continues.
Tachyphylaxis
Response falling away rapidly over a few administrations rather than gradually, which separates it from slower desensitization. Reports of it appear with melanocortin agonists and with some growth hormone releasing peptides.