Business Insider reports that there is a lack of research indicating that melatonin is a safe sleep aid for pregnant women.

One meta-analysis published in 2013 in PLOS ONE, found that while melatonin’s effect on sleep was modest, it led to improved sleep quality, increased time spent sleeping, and a decrease in how long it took people to fall asleep. The study described the effect of melatonin on sleep as “modest.” And, as the National Sleep Foundation notes, many studies fail to show that melatonin is more helpful than a placebo.

“Data is not convincing that melatonin supplements are effective but doses available in the over-the-counter products appear to be safe,” says Lynn L. Simpson, MD, FACOG, the chief of Obstetrics at Columbia University Medical Center.

Likewise, taking melatonin supplements while pregnant is not recommended due to a lack of research on its effects.