Melatonin is a naturally occurring hormone synthesized primarily by the pineal gland to regulate the sleep-wake cycle. Its production increases in the evening, signaling the body that it is time to sleep. As a widely available over-the-counter dietary supplement, it is commonly used by people seeking temporary relief from insomnia, jet lag, or shift work disorder. Understanding its safety profile and the potential consequences of excessive intake is important for consumers due to its non-prescription status and widespread use.
Melatonin’s High Safety Profile and Theoretical Toxicity
A definitive fatal dose of melatonin in humans has not been established, a fact that speaks to its extremely high therapeutic index. This high index means the dose required to produce a toxic or lethal effect is vastly greater than the dose needed for a therapeutic effect. In preclinical animal studies, researchers have been unable to find a lethal dose 50% (LD50). The doses used in animal toxicology studies are often astronomically high when compared to the standard human dose, which typically ranges from one to ten milligrams. The primary danger associated with taking excessively high amounts is not sudden organ failure, but rather the severe, non-lethal side effects and the risk of injury resulting from profound sedation.
Recognizing and Managing Acute Overdose Symptoms
A single, massive intake of melatonin, referred to as an acute overdose, typically leads to immediate, non-life-threatening, but highly unpleasant symptoms. The most common effects involve the central nervous system, resulting in profound drowsiness, extreme sedation, and disorientation. This intense sleepiness poses an indirect danger, as it increases the risk of accidental injury or falls, especially in older adults. Gastrointestinal symptoms frequently accompany an acute overdose, including nausea, vomiting, and diarrhea. Other physical manifestations can involve severe headache, dizziness, and mild changes in blood pressure or heart rate.
Treatment for a suspected acute overdose is primarily supportive care, which focuses on managing the symptoms until the body clears the excess hormone. If a single massive ingestion is suspected, contacting Poison Control or seeking emergency medical attention is advisable. This is particularly important if symptoms like difficulty breathing, seizures, or loss of consciousness occur.
Understanding Long-Term Effects of Excessive Dosing
Regularly taking doses significantly higher than recommended over an extended period can lead to chronic health consequences distinct from an acute overdose. A common long-term effect is the “melatonin hangover,” which presents as excessive daytime grogginess, fatigue, and reduced alertness. This persistent sedation can impair cognitive and motor function, affecting daily activities. Chronic high-dose melatonin use can lead to hormonal disruption by suppressing the body’s natural production. This suppression makes it difficult to maintain normal sleep cycles if the supplement is stopped.
Increased Risk in Specific Populations and Drug Interactions
Certain groups are disproportionately vulnerable to adverse effects from melatonin, even at standard or moderately elevated doses. Children are at increased risk because external supplementation may adversely affect gonadal development. The elderly are also more sensitive to the sedative effects, which increases their risk for falls and confusion. They may require lower doses due to a naturally lower baseline level of the hormone.
Melatonin engages in several dangerous drug interactions that increase the risk of serious complications. It can potentiate the effects of blood thinners, such as warfarin, by slowing blood clotting and increasing the risk of severe bleeding. Combining melatonin with central nervous system depressants, including sedatives, tranquilizers, and alcohol, can lead to dangerously high levels of sedation and respiratory depression. Melatonin may also interfere with the efficacy of other medications:
- Medications for diabetes.
- Medications for high blood pressure.
- Anticonvulsants, potentially increasing the frequency of seizures.