Which hormone is known to induce sleep?

Melatonin is a hormone that plays a crucial role in regulating sleep-wake cycles, often referred to as the circadian rhythm. It is produced by the pineal gland in the brain, primarily in response to darkness. As light diminishes, melatonin levels increase, signaling to the body that it is time to prepare for sleep. This biological process helps facilitate the transition into sleep and maintains overall sleep quality.

The other hormones listed have different primary functions: serotonin is involved in mood regulation and can influence sleep indirectly; cortisol is known as the stress hormone, which can disrupt sleep patterns when its levels are elevated; dopamine is associated with reward and pleasure, rather than directly inducing sleep. Melatonin’s specific role in promoting sleep sets it apart as the correct answer.