Melatonin Interactions

Alcohol can increase drowsiness from melatonin and reduce sleep quality.

Caffeine counteracts melatonin and can delay sleep onset.

Propranolol blocks pineal beta-1 adrenergic receptors that control endogenous melatonin synthesis, suppressing nighttime melatonin levels by roughly 50% and contributing to insomnia, vivid dreams, and reduced sleep efficiency. Low-dose oral melatonin at bedtime can restore sleep architecture without compromising propranolol's antihypertensive effect.

Metoprolol blocks the beta-1 adrenergic receptors that drive pineal melatonin synthesis, suppressing endogenous nighttime melatonin and contributing to insomnia, vivid dreams, and reduced sleep efficiency. Low-dose oral melatonin can restore sleep without interfering with metoprolol's cardiovascular benefits.

Combining the Z-drug hypnotic zolpidem with melatonin can produce additive next-day drowsiness, impaired thinking, and reduced motor coordination, with the risk most pronounced in older adults. The interaction is primarily pharmacodynamic.

Melatonin and alprazolam both promote sleep and can produce additive sedation, impaired alertness, and reduced motor coordination when used together. The combination may increase next-day drowsiness and risk during activities like driving.

Both diphenhydramine and melatonin cause sedation through different mechanisms (H1 antagonism and MT1/MT2 agonism). Combined use produces additive CNS depression, next-day drowsiness, impaired cognition, and increased fall risk, especially in older adults.

Melatonin signals the brain that it is biological night through MT1 and MT2 receptors in the suprachiasmatic nucleus, while magnesium acts as a NMDA antagonist and GABA-A agonist, helping the nervous system actually relax around that signal. A double-blind RCT in nursing home residents with primary insomnia (Rondanelli 2011) found that nightly melatonin 5 mg + magnesium 225 mg + zinc 11.25 mg significantly improved sleep quality, ease of falling asleep, and morning alertness versus placebo.