Final answer:
Prozac, a selective serotonin reuptake inhibitor, increases serotonin levels in the brain and indirectly has an agonistic effect on serotonin activity, which can alleviate symptoms of depression.
Step-by-step explanation:
The drug that affects mood, hunger, sleep, and arousal, with an undersupply linked to depression, and which is increased by drugs such as Prozac, is serotonin. Prozac is known as a selective serotonin reuptake inhibitor (SSRI), which works by inhibiting the reuptake of serotonin in the brain, making more serotonin available in the synaptic gap between neurons. This action can help alleviate depressive symptoms by enhancing communication between neurons in brain circuits that regulate mood.
Regarding the question of whether Prozac is an agonist or antagonist, Prozac acts as a serotonin reuptake inhibitor, making it neither a direct agonist nor antagonist. Instead, it indirectly increases the levels of serotonin available for synaptic transmission, thus having an agonistic effect on serotonin activity.