Thankfully, we’re not talking about the stuff used to fire up your barbecue. Activated charcoal is ash that’s been heated to high temps, then treated with steam or other natural activating agents like phosphoric acid until it becomes a highly porous powder. The end result is a substance that acts like a magnet in your body for junk like toxins, heavy metals such as mercury, and even bloat-causing gas. And since activated charcoal isn’t absorbed by your digestive tract, it—and all the gunk it picks up—passes right through you. Activated charcoal isn’t new: Health food stores have stocked it in supplement form forever, while holistic practitioners have used it as an antidote for poisoning for years. But now, juice bars in trendy urban areas like New York, L.A., and Austin are blending the powder with just purified water, lemon juice, and natural sweeteners to make a lemonade cleanser with a deep inky hue. (By itself, charcoal is surprisingly tasteless.)   MORE: Coconut Water Is Lame: Five New Drinks That Are Way Healthier Why put charcoal in lemon juice and not an antioxidant-rich green blend like kale? “The reason we put charcoal in something neutral instead of in a green juice is because charcoal doesn’t know what’s good and what’s bad, and you don’t want it to pull out good nutrients, too,” says Danielle Sobel, founder of Juice Society in Austin. In other words, activated charcoal is so awesome at soaking up stuff in your body that it might just as likely bind to beneficial nutrients or medications as well as harmful toxins. To help diminish these effects, experts recommend taking anything with activated charcoal on an empty stomach—or at the very least, an hour or two before or after eating. So you should you try charcoal juice? Sadly, there’s no hard scientific evidence to support the detox claim, says Caroline Cederquist, M.D., founder of bistroMD . But some research does suggest that activated charcoal’s ability to reduce gas and bloating are legit, so it’s worth a shot if you suffer from occasional digestive distress. (Though if your stomach problems are frequent or severe, it’s probably better to work with your doc to figure out the root cause.) MORE: What’s Really In Your Starbucks Coconut Milk Latte? Even then, whether you buy bottled charcoal lemonade or mix a capsule of activated charcoal with water at home (which might not taste as delicious, but works just the same), proceed with caution: Consuming too much can cause constipation because charcoal sucks up water, along with everything else. “I’d take it intermittently rather than daily, and drink significantly more water and eat more high-fiber foods throughout the day,” says Renee Rosen, a certified holistic nutritionist and founder of the wellness consulting company Green Eggs & Kale. Also, check the label or ask at your local juice bar to make sure your charcoal is pure before you drink or take it: Many charcoals are derived from natural sources like coconut husks, peat, or wood, but some can also come from petroleum. MORE: Coconut, Birch, Or Maple: Which Tree Water Is Best?