MCAT Psych/Soc Practice Exam – All-in-One Guide to Master Psychological, Social, and Biological Foundations of Behavior 2026

The hormone that stimulates the drive for sleep is melatonin. This hormone is produced by the pineal gland in response to darkness, and its levels increase in the evening, promoting the onset of sleep. Melatonin helps regulate the body's circadian rhythms, signaling to the body that it is time to prepare for sleep. This process is essential for maintaining a regular sleep-wake cycle and ensuring restorative sleep.

Cortisol, on the other hand, is often referred to as the "stress hormone" and typically peaks in the morning to help promote wakefulness and alertness. Serotonin is a neurotransmitter that can be converted into melatonin but primarily plays a role in mood regulation. Dopamine is associated with motivation and reward, influencing behaviors and feelings of pleasure rather than directly stimulating sleep. Thus, melatonin is uniquely positioned as the key hormone that induces sleepiness in the body.