Final answer:
Lysergic acid diethylamide (LSD) activates serotonin receptors in the brain, namely the 5-HT2A subtype, leading to its psychedelic effects.
Step-by-step explanation:
The receptor type activated by lysergic acid diethylamide (LSD) is the serotonin receptor, specifically the serotonin 2A (5-HT2A) receptor subtype. LSD is known to act as a serotonin agonist and has a high affinity for these receptors, which are distributed throughout the brain and contribute to various functions, including mood, perception, and cognition. This interaction with serotonin receptors is responsible for LSD's well-known psychedelic effects.