Dream Water. You’ve probably seen the popular zero-calorie sleep and relaxation shots at your local CVS, Walgreens or the airport.

A Miami company launched this product in 2009, and it's now being sold at 20,000 spots all over the country.

Some celebrities have Tweeted about it. Dream Water was featured on the Today show and Kathie Lee Gifford is a fan.

But what’s in Dream Water?

NBC Miami asked Dr. Damon Salzman of United Sleep Diagnostics to check out the main ingredients: GABA, melatonin and L5-hydroxytryptophan.

He explained that GABA is a neurotransmitter in the brain that deals with relaxation. Melatonin is a brain hormone that works with your body’s natural clock for bedtime, and 5-HTP increases the production of serotonin, a mood lifter.

"The amount of ingredients strikes me actually as being very safe,” Salzman said.

He advises not to combine it with alcohol, and says some antidepressants and sedatives might interact with the ingredients.

The product box warns, “Do not operate machinery or other important tasks when taking this product.” It also says to consult with your doctor before using it if you have any medical condition or take medications.

Because Dream Water is a dietary supplement, the Food and Drug Administration does not evaluate it.

Want to give your take? Join the conversation on our NBC Miami Facebook page, where we asked for comments from people who have used Dream Water. Most of the feedback so far is positive.