Last updated on March 6th, 2020
Melatonin is an amazing hormone that is available in supplement form for those who need a little help sleeping. But, just like any drug or supplement, melatonin isn’t without its side effects.
That doesn’t mean that melatonin side effects make the supplement unsafe. It just means that you should educate yourself about the side effects of melatonin before you start using it. When you know what to expect, including common melatonin side effects, you’re better able to understand how melatonin can affect your body.
If you’re considering using melatonin as a sleep aid — or for another reason — here’s a rundown of everything you need to know about possible melatonin side effects.
Long-Term Effects of Melatonin
Melatonin is a hormone produced naturally in the body. Supplements are available over the counter and without a prescription, which makes melatonin one of the most popular and readily available sleep aids in the world. Because melatonin is natural, its effects are much more likely to be experienced over the long-term rather than immediately. Here’s a look at some of the long-term side effects of melatonin.
Believe it or not, the long-term use of melatonin is associated with weight loss. A 2003 study  found that lab rats whose melatonin-producing gland was removed experienced weight gain. Conversely, overweight rats given melatonin as a supplement lost weight — even when their diets stayed the same.
Melatonin has been called a miracle hormone, and it has many uses beyond just aiding with sleep. One of the non-traditional uses of melatonin is to lower nighttime blood pressure.
Anyone’s blood pressure is likely to fluctuate over the course of 24 hours. Blood pressure tends to be higher during the day and lower at night. That said, some people see huge dips in blood pressure at night while others see only small shifts.
For anyone who experiences only a small shift, the use of melatonin can promote the dipping process  and help lower nighttime blood pressure — which is good for sleep and good for the heart.
One important caveat: If you’re already taking medication to control your blood pressure, melatonin may interact with your medication to actually raise your blood pressure. Make sure to look up melatonin interactions or to talk to your doctor before using.
For some, melatonin can really affect the stomach and the digestive system. Gastrointestinal issues when using melatonin may include:
- Stomach aches
- Unusual stools
Before you let these gastrointestinal issues scare you away from using melatonin as a supplement, you should know that these types of issues rarely emerge as side effects of melatonin. It’s possible you may experience them, but it’s also unlikely.
One common thread of melatonin side effects is that they often enhance issues you’re already experiencing. That holds true for depression, whose existing symptoms may be enhanced by the use of melatonin.
Even if you don’t suffer from depression, melatonin can lead to mood swings in either direction. You may find that you feel sadder or more giddy than usual. In extreme cases, the use of melatonin can lead to paranoia and even hallucinations.
It’s essential that you understand the right melatonin dosage for you and your body. In most cases, the most extreme side effects of melatonin can be avoided when you optimize your dosage.
There’s one very important melatonin side effect to consider before engaging in long-term use. If you choose to use melatonin over time, it may stop being effective — and then it may even start having the opposite of the desired effect.
At the heart of the problem is your body’s ability to adjust to its circumstances. If you are consistently supplementing with melatonin, your body may get use to that dosage and grow immune to its impact.
Most experts recommend using melatonin only when needed to get back on schedule or to fight jet lag. If you’re using melatonin for ongoing sleeping issues, consider using it for no more than 4 weeks at a time. If your symptoms persist beyond that 4-week period, consult your primary care physician about another course of action.
Side Effects by Age
Melatonin side effects also vary by age. If you’re an adult, you are more prone to certain side effects than if you’re taking it as a child. The same is true of the elderly who choose to use melatonin — they may experience unique side effects, too. Here’s a look at all you need to know about the side effects of melatonin by age:
It’s important for the elderly to seek medical guidance before using melatonin as a sleep aid. Yes, melatonin is typically safer to use than other sleep aids, but it may have some unique side effects that only impact the elderly.
One important example is how melatonin side effects may be harmful to those in the early stages of dementia or suffering from other memory-related issues. Furthermore, older adults tend to take more medications, which can increase the likelihood of an unsafe interaction.
Melatonin is safest for adults, though they may still experience many of the melatonin side effects listed above. Awareness is of the utmost importance. Be attuned to how melatonin is affecting your body and what side effects you’re experiencing, and you’ll be able to optimize your dosage or to cease using the supplement if needed.
One last warning on the side effects of melatonin for adults: Be particularly careful when using melatonin with marijuana, alcohol or even caffeine. These substances may exacerbate existing melatonin side effects, making them more acute and more harmful to your health. In fact, it’s best to avoid marijuana, alcohol and caffeine altogether when using melatonin.
Children, Toddlers and Babies
Parents should be particularly careful when using melatonin for children, toddlers and babies. In some cases and in some dosages, melatonin can be a helpful and effective supplement for young people. That said, used inappropriately or given in too large a dose, melatonin can lead to seizures and other side effects that all parents will want to avoid.
Brad is a freelance writer and journalist who lives and works in Austin, TX. Away from work, he enjoys running, reading, watching baseball and spending time with his family. On rare occasions when he gets the chance, he loves nothing more than a long nap on a Sunday afternoon.