Melatonin (immediate-release) is an over-the-counter sleep aid used to help with insomnia, particularly difficulty falling asleep. It works by mimicking the body’s natural melatonin hormone, signaling that it’s time to initiate sleep. Immediate-release formulations act quickly, making them most useful for sleep onset insomnia, but they are less effective for staying asleep through the night. It is generally well tolerated, with possible side effects including daytime drowsiness, vivid dreams, or headache. Melatonin is often used as a first-line or adjunct to behavioral strategies like CBT-I, especially for short-term or circadian-related sleep issues.