Final answer:
Direct action by drugs refers to when a drug binds directly to a specific receptor in the body, leading to a physiological response. Indirect action involves drugs that affect the release, synthesis, or metabolism of neurotransmitters. The effects of direct action drugs are more immediate and specific, while indirect action drugs may have more widespread effects.
Step-by-step explanation:
Direct action by drugs refers to when a drug binds directly to a specific receptor in the body, leading to a physiological response. For example, opioids like morphine bind to opioid receptors in the brain to relieve pain. Indirect action, on the other hand, involves drugs that affect the release, synthesis, or metabolism of neurotransmitters, rather than directly binding to receptors. An example of indirect action is selective serotonin reuptake inhibitors (SSRIs) which increase the levels of serotonin in the brain by inhibiting its reuptake.
In terms of effects on the body, direct action by drugs can produce a more immediate and specific response. The effects are often more targeted and can be felt quickly. Indirect action, on the other hand, may have more widespread effects as it affects the overall balance of neurotransmitters in the brain. The onset of the effects may be slower compared to direct action drugs.