While severe side effects are unlikely, taking too much melatonin at once can disrupt your sleep-wake cycle and could result in next day grogginess. Because each person’s sleep cycle is different, as well as each person’s height, weight and sensitivity to hormones, there is no one-size-fits-all dose of melatonin that will work for everyone. Our ZzzQuil PURE Zzzs have an optimal 1-2 mg of melatonin in each dose. It’s best to start with a low dose of melatonin as experts, from researchers from MIT to Dr. Oz, recommend. If you give your body more than it needs, it’s possible to have the opposite effect and disrupt your sleep-wake rhythm, making it even more difficult to fall asleep.