Final answer:
Psychoactive drugs can act as agonists or antagonists for neurotransmitter systems. LSD acts as an agonist, mimicking a neurotransmitter.
Step-by-step explanation:
Psychoactive drugs can act as agonists or antagonists for a given neurotransmitter system. Agonists are chemicals that mimic a neurotransmitter at the receptor site. An antagonist, on the other hand, blocks or impedes the normal activity of a neurotransmitter at the receptor.
LSD is acting as an agonist, which mimics a neurotransmitter.