Final answer:
Psychoactive drugs affect the human body by interacting with neurotransmitters or neurotransmitter receptors in the brain. Natural counterparts to the sensations or feelings created by drugs can be found in the brain's own neurotransmitter systems. Exercise can stimulate the release of chemicals that can produce similar sensations to those caused by drugs.
Step-by-step explanation:
Psychoactive drugs affect the human body by interacting with neurotransmitters or neurotransmitter receptors in the brain. These drugs can act as either agonists, increasing the activity of neurotransmitters, or antagonists, blocking or impeding neurotransmitter activity. Natural counterparts to the sensations or feelings created by drugs can be found in the brain's own neurotransmitter systems, which can be stimulated through activities like exercise.