Final answer:
Alcohol is the depressant drug that can loosen inhibitions and impair memory, functioning mainly by suppressing the central nervous system and affecting the GABA neurotransmitter system.
Step-by-step explanation:
A depressant is a type of psychoactive drug that calms the brain, reduces anxious feelings, and can induce sleepiness. In the context of the student's question, alcohol is a prominent depressant that can loosen inhibitions and impair memory. Alcohol, as a depressant drug, tends to suppress central nervous system activity, resulting in a range of effects from mild sedation to severe respiratory depression depending on the dosage. Alongside alcohol, other depressants such as barbiturates and benzodiazepines also function as GABA agonists, which contributes to their effect of reducing arousal and causing sedation.
At lower doses, alcohol may lead to relaxation and decreased inhibitions, while higher doses can induce more severe symptoms such as memory loss and motor disturbances. The consumption of alcohol, particularly in high doses, has serious health implications that can result in coma or even death.