What drug enters the brain rapidly and can slow thought processes and memory?

Heroin is a powerful opioid that, when administered, can quickly cross the blood-brain barrier and affect the central nervous system. Once it enters the brain, heroin is converted to morphine, which binds to opioid receptors, leading to effects such as euphoria, drowsiness, and a significant alteration in cognitive functions. This rapid onset of action can impair thought processes and memory, as it inhibits certain neurotransmitters involved in these cognitive abilities.

Marijuana has psychedelic effects, but its impact on thought processes and memory often develops more gradually, and its active ingredient, THC, affects the brain in a different manner compared to heroin. Cocaine primarily acts as a stimulant, leading to increased energy and alertness rather than a slowing of thought processes. Inhalants, although they can have sedative effects, do not act as rapidly in the brain as heroin does. Therefore, heroin stands out as the correct answer for a drug that quickly slows thought processes and memory due to its fast absorption and potent effects on brain function.