An agonist is a drug that mimics or increases the effect of a neurotransmitter.
An agonist drug works in a way that it binds itself to a receptor inside the cell or in its surface and then modifies the cells' function, where it amplifies or imitates the neurotransmitter.
There are many negative effects of agonist drugs. For instance, one experiences symptoms like trembling, nervousness and tension, headaches, palpitations and muscle cramps. Apart from this, it also causes nausea, hypertension and cardiac arrhythmia.
Agonist drugs can be of three kinds, full agonist, co agonist and selective agonist. Some examples of agonist drugs include heroin, morphine and opium.
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