Final answer:
Psychoactive drugs act as either agonists or antagonists to neurotransmitters in the brain, but they do not alter the basic structure of brain cells or genetic code within neurons.
Step-by-step explanation:
Psychoactive drugs achieve their effects by influencing brain chemistry, but not all mechanisms are means through which these drugs exert their influence. Generally, psychoactive drugs act as agonists, which enhance the activity of particular neurotransmitters, or as antagonists, which decrease neurotransmitter activity. These drugs can promote neurotransmitter synthesis, reduce their reuptake, or mimic their action by binding to receptors. However, psychoactive drugs do not directly perform functions outside of the realm of affecting neurotransmitters, such as changing the basic structure of brain cells or altering the genetic code within neurons.