# Agonist and antagonist

Source: https://onco.cc/terms/agonist-antagonist/  
OnCo record `agonist-antagonist` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

An agonist switches a receptor on, imitating the natural signal; an antagonist sits in the receptor and blocks it without switching it on. Cancer medicine uses both.

## Summary

Antagonists are the more familiar: tamoxifen and fulvestrant occupy the oestrogen receptor so oestrogen cannot, and enzalutamide does the same to the androgen receptor. Agonists are used when switching something on helps, such as STING agonists that alarm the innate immune system, CD40 or 4-1BB agonists that stimulate immune cells, and GnRH agonists that paradoxically shut down testosterone production by overstimulating the pituitary. Partial agonists and selective modulators (SERMs) fall in between, activating a receptor in some tissues while blocking it in others.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: agonist; agonists; antagonist; antagonists; receptor agonist; receptor antagonist; receptor agonists

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Agonist
- Wikipedia: https://en.wikipedia.org/wiki/Agonist

## Connected records

- terms: [Hormone therapy](https://onco.cc/terms/hormone-therapy/), [Inhibitor](https://onco.cc/terms/inhibitor/), [Ligand](https://onco.cc/terms/ligand/), [Receptor](https://onco.cc/terms/receptor/)
- technologies: [Androgen deprivation & AR pathway inhibitors](https://onco.cc/technologies/androgen-deprivation/), [Endocrine therapy (SERMs, AIs, SERDs)](https://onco.cc/technologies/endocrine-therapy/), [STING & innate immune agonists](https://onco.cc/technologies/sting-agonist/)
- targets: [Androgen receptor](https://onco.cc/targets/androgen-receptor/), [Estrogen receptor (ERα)](https://onco.cc/targets/estrogen-receptor/)

---
JSON: https://onco.cc/api/v1/entities/agonist-antagonist.json