Question

drugs that combat depression by affecting the levels or activity of neurotransmitters
amobarbitals
bupropions
alprazolams
antidepressants
olanzapines

Explanation:

Antidepressants are drugs that combat depression by affecting neurotransmitter levels or activity. Amobarbitals are barbiturates (sedatives/hypnotics). Bupropions are a type of antidepressant but the general term is more appropriate here. Alprazolams are benzodiazepines (anxiolytics). Olanzapines are antipsychotics.

Answer:

antidepressants