Final answer:
Opiates and similar drugs typically work by mimicking neurotransmitters, which is an agonist action where the drug activates the neurotransmitter receptor in a similar manner to the natural neurotransmitter.
Step-by-step explanation:
The student has asked a question about the mechanism by which opiates and other drugs interact with receptor sites in the brain. Specifically, opiates and similar drugs occupy receptor sites by mimicking neurotransmitters. This is referred to as an agonist action, where the drug binds to the neurotransmitter receptor and activates it, just as the natural neurotransmitter would do.
Drugs that act as agonists can have a variety of effects on neurotransmitter systems, such as promoting the synthesis of neurotransmitters, reducing their reuptake from synapses, or, as in the case with opiates, mimicking their action by binding directly to the neurotransmitter receptors.
Antagonists, by contrast, work by blocking neurotransmitter receptors, thus inhibiting the neurotransmitter's normal effects. An example of this is how selective serotonin reuptake inhibitors (SSRIs) prevent the reuptake of serotonin, thus enhancing its effects in the brain.