The hormone from the pineal gland that promotes sleepiness is

• A. Adrenaline
• B. Melatonin
• C. Serotonin
• D. Dopamine

Answer: (B)

Melatonin is the hormone produced by the pineal gland that promotes sleepiness. Its levels rise in the dark and help signal to the body that it’s time to wind down, supporting the sleep-wake cycle. Serotonin in the pineal gland is converted into melatonin, and the amount of melatonin released is controlled by light exposure: light seen by the eyes ultimately suppresses its production, while darkness allows it to increase. Adrenaline comes from the adrenal gland and is tied to alertness and the fight-or-flight response; serotonin and dopamine are important neurotransmitters involved in mood and reward, not the sleep-promoting signal from the pineal gland. So melatonin best explains the sleepiness effect.