Does Melatonin Cause Weight Gain?  

Discover the truth about the connection between melatonin and weight gain. Learn how to make informed decisions about your sleep and weight goals.
Medical Reviewer: Elizabeth Lowden, MD
Published on: June 28, 2023
Updated on: March 5, 2024

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Taking melatonin can be helpful to those who have trouble falling or staying asleep at night.


If you are taking melatonin to help you get better sleep, you may have heard there is a link between the supplement and weight gain. Some information found online suggests a link exists between melatonin and weight gain. However, there is no data to support this association. Rather, it is lack of sleep (for which many take melatonin supplements) that can contribute to weight gain. This article will explore the true relationship between weight, melatonin, and sleep, and provide guidance to those struggling with both weight and sleep issues. 

What is Melatonin?

Melatonin is a key naturally- produced hormone that helps regulate the circadian rhythm, which is our body’s internal 24-hour clock that coordinates biological processes so they occur at the correct time of day. Melatonin is released by the pineal gland in the brain in response to darkness and helps trigger the onset of sleep. Melatonin levels see-saw with cortisol levels, with melatonin peaking in the early nighttime hours when cortisol is lowest, and decreasing in the early morning hours when cortisol is highest. The release of melatonin decreases with age and is reduced in states of insulin resistance. It is also a very popular over-the-counter sleep aid, with melatonin use increasing five-fold in the last two decades.

What Does Science Say about Melatonin and Weight Gain?

Despite its popularity, concerns have arisen around the possibility that melatonin supplements cause weight gain. This fear is extrapolated from the observation that rats who were given high doses of melatonin (equivalent to 7 to 70g in a 150lb person) experienced decreased intestinal motility (i.e. how fast they digested food), though intestinal motility was found to increase when the rats were given lower doses of melatonin. The thinking is that slowed digestion might translate into weight gain.

However, animal studies have shown that melatonin supplementation can actually lead to weight loss, or at least prevent weight gain in situations like eating a high-fat diet or during the menopausal transition. One proposed mechanism by which melatonin may lead to weight loss is by increasing brown adipose tissue, a special type of fat that helps regulate body temperature by burning calories as heat (as opposed to white adipose tissue, the more common type of fat that principally serves to store calories for later use), though only very small studies on humans have corroborated this phenomenon. And while it is true that large clinical trials supporting melatonin as a treatment for obesity are lacking, importantly, there is no evidence to support a link between melatonin supplementation and weight gain. 

Those who started melatonin supplementation and saw weight gain should look at other culprits, such as lifestyle changes, stress, and poor sleep – the reason they likely started the melatonin supplementation in the first place (see our blog post Does Coffee Make You Gain Weight? to explore the truth behind similar fears connecting caffeine and weight gain). 

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How Melatonin Affects Sleep and Weight

Though there is insufficient evidence to recommend melatonin for all patients with insomnia, some people may see improvements in their overall sleep quality and quantity after starting melatonin supplements. Especially for those people with misaligned circadian rhythms due to shift work or jet lag, as well as older individuals who produce less melatonin on their own, melatonin supplements can improve overall sleep.

One thing that is clear is that getting enough high quality sleep is very important for weight management and overall health. Indeed, the bidirectional relationship between poor or inadequate sleep and weight gain couldn’t be clearer. Not getting enough sleep increases one’s future risk of obesity, and obesity – by increasing the risk of sleep apnea – can increase the likelihood of future poor sleep. (Check out our blog post Why Does Sleep Apnea Cause Weight Gain?  to explore the relationship between weight gain and sleep apnea). Lack of sleep is associated with higher levels of ghrelin, the hormone that drives up hunger, and lower levels of leptin, the hormone that signals to the brain that you’re full.

The impact of these hormonal changes was observed in a study where young, healthy weight individuals were studied for two separate periods of 14 days, one in which they only had a four hour sleep opportunity and another in which they had a nine hour sleep opportunity. The study found that sleep restriction resulted in consumption of more than 300 more calories per day and one pound of fat gain (with statistically significant increases in visceral fat, the unhealthy fat that increases the risk of metabolic health problems like high blood pressure and diabetes), with no difference in total energy expenditure. A meta-analysis of 30 studies involving over 600,000 participants showed an increase in BMI of 0.35 (about 3 pounds) for every reduction in one hour of sleep below eight.

Put Your Melatonin Worries to Sleep 

Melatonin does not cause weight gain. In fact, if it helps improve the quality and quantity of your sleep, it can actually help promote weight loss. Poor sleep is just one of many reasons for not being able to lose weight. If you feel like you are not seeing the results you want despite your best efforts to lose weight, FORM can help! 

Our Board Certified Doctors and Registered Dieticians will take the time to get to know you and carefully evaluate all factors that may be contributing to your weight gain or inability to lose weight. Once your clinical Care Team has reviewed your lifestyle, medical history, and needs, they will develop a personalized plan to help you reach your weight loss goals, which may include a prescription for FDA-approved weight loss medication,when appropriate. If you’re looking for individualized guidance to achieve a healthy weight, the FORM medical weight loss program may be right for you.

Take our quiz to find out if you’re a candidate today, or schedule a call/send a message to get in touch with us directly.

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