I also wondered when I saw these words in the documents for drug addiction treatment. They said that an agonist has an effect, and an antagonist does not, but there was no further explanation. I wonder what antagonists are used for - or is it simply to relieve the effects of toxic substances?

Here’s what we found: an agonist is a drug that activates receptors in the brain or body, causing an effect similar to the natural one. An antagonist, on the other hand, is a blocker, preventing another substance from activating the same receptors. For example, methadone is an agonist, which replaces the effects of heroin, reducing withdrawal, and naltrexone is an antagonist, which blocks opioid receptors and reduces the effects of the substance. Information with a detailed explanation is available here: https://unitedrecoveryproject.com/rehab-blog/agonist-vs-antagonist-drugs/ — a very useful article about their roles in therapy and addiction.