Melatonin, a.k.a. the sleepy hormone, is produced naturally by the body and—you guessed it—plays a major role in sleep. “The release of natural melatonin in your body is linked to the time of day, but it typically increases when it’s dark and decreases during periods of more light,” says Melissa Rifkin, MS, RDN, CDN.

This is because melatonin helps govern your body’s circadian rhythm—aka its sleep-wake cycle—so when you release melatonin, it’s basically a biological signal to hit the hay. “Melatonin in our brains helps us get sleepy,” clinical psychologist and sleep specialist Shelby Harris, PsyD, author of The Women’s Guide to Overcoming Insomnia, previously told Well+Good.

To help enhance the brain’s natural melatonin and induce sleepiness, some folks turn to taking melatonin in pill form (though it is found naturally in certain foods, including pistachios). “Taking melatonin may improve sleep in those with certain sleep disorders, like insomnia, and others who have a hard time falling asleep,” says Rifkin. “Research also suggests supplemental melatonin may aid those who are experiencing jet lag symptoms.”

The issue, Rifkin says, is that oftentimes people take way too much melatonin. Furthermore, experts do warn against nightly use of it, citing reasons like risk of dependence and an overriding of the body’s natural response that they don’t advise. While melatonin has been shown to be safe for short-term use, there isn’t enough research to show that it’s safe for long-term use.

“The ideal dose of melatonin for an adult ranges from 0.5 to five milligrams [per the National Sleep Foundation], and it should be taken 30 minutes to one hour before bedtime,” behavioral sleep specialist Carleara Weiss, PhD, sleep science advisor for Aeroflow Sleep, told Well+Good. “Doses higher than optimal—that is, five milligrams at a time—can lead to dizziness, headaches, and nausea, and some people may experience changes in blood pressure, vivid dreams, or nightmares.”

What’s more, there’s some research that has shown that melatonin supplements sometimes contain false dose labeling making long-term use all the riskier: A 2017 study published in the Journal of Clinical Sleep Medicine found that the content of more than 70 percent of melatonin supplements varied by as much as 83 percent less to 478 percent more than what was listed on the bottle. Researchers also found that over a quarter of supplements tested contained serotonin, which if taken consistently long-term, can negatively impact the heart, the brain and more. “Choosing a supplement is never easy in a cluttered, unregulated market,” says Rifkin, who underlines that the most important thing is to look for one with few to no chemically-based and artificial ingredients. “Additionally, look for products that use scientific backing when developing products. They should also be inspected by the United States Pharmacopeial Convention, which will often say ‘USP-verified.’ Monat Sleep Drops are a great example of an excellent-quality supplement with no artificial sweeteners and a science-backed development.”

Most importantly, be sure to consult with a physician before starting on any supplements, including melatonin. And if you’re new to taking melatonin, Rifkin recommends starting on the lower end of the range and adjust your dosage as needed—and keeping an eye on the symptoms below.

Here’s how your body is telling you that you may be taking too much melatonin

1. It’s no longer working

“Taking too much melatonin may interfere with your body’s circadian rhythm, causing more sleep problems,” says Rifkin. “Additionally, some people may be more sensitive than others to the effects of melatonin, which is why it’s best to start with a one milligram dose and increase only as needed.”

2. You’re groggy

“Taking too much melatonin may lead to symptoms, like grogginess during the day and nightmares while sleeping,” says Rifkin.

3. Your mood is off

Rifkin notes that some people who take melatonin report symptoms like diarrhea, irritability, nausea, and dizziness. It can also potentially aggravate depression and anxiety.

4. Your blood pressure is up

“Too much supplemental melatonin could even impact your blood pressure, another reason why it’s important to speak with a doctor about taking melatonin if you’re currently taking medication, including those that reduce blood pressure,” says Rifkin.