After almost a decade of amazing sales in the energy drink sector, a new selection of relaxation drinks are slowly making their way to store shelves. With names like Dream Water, iChill, and RelaxZen, marketers are attempting to attract teens who are trying to wind down and adults who have difficulties falling asleep.

So far the relaxation drinks account for about $20 million in sales per year, which is pretty impressive but leagues behind the $5 billion that energy drinks pull in annually. Their popularity is growing, but so are concerns for the sleep-inducing melatonin that is one of the main ingredients in the drinks.

Last month the Food and Drug Administration ordered the makers of Drank, a melatonin based drink which launched in 2008, to prove that using melatonin, a hormone found naturally in the human body, is safe. It has 2 milligrams of melatonin, which is 20 times the amount found in the body naturally.

Melatonin is also sold in pill form and can be found in the vitamin section of nearly any grocery or drug store, with melatonin amounts ranging from 3 millgrams to 10 milligrams. There are concerns, however, about having the hormone in drink form because often times the amount one consumes of a beverage is dependent on its taste and their thirst, rather than being taken as needed like any other drug.

Experts indicate that there have not yet been any reliable studies to determine the impact of melatonin on adults or children.