Search for the hashtag “teatox” on Instagram and you’ll find more than 80,000 posts, from brands and  enthusiastic consumers alike, raving about the weight loss benefits of drinking certain herbal tea concoctions. The new tea detox craze, which has gone viral thanks to social media, promises to put women on the fast track to a better body, boosting their metabolism, giving them more energy, aiding in fat burning and even clearing up their skin. But at what cost to their health?

“Dietary supplements like tea aren’t really regulated so you can pretty much make whatever kind of claims you want,” points out Margaret Wertheim, a registered dietitian in private practice in Madison, Wisconsin. There are tons of brands on the market offering their own teatox brews, including Skinny Teatox, Bootea, Kusmi Tea, Swami Mami and Detox Skinny Herb Tea, which promises to “help you to achieve your dream silhouette quicker without exposing you to [a] diet regime and hard physical training.”

However, several teatoxing brands “help” you lose weight with the ingredient senna leaf, a natural laxative that basically works by irritating the lining of the bowel and can cause stomach cramps and diarrhea.

And yes, while it might make you feel skinny temporarily, it’s important to keep in mind that weight loss achieved by relieving constipation is not fat loss, notes Wertheim. “People may think that they are losing weight because they are getting cleaned out,” she says. In reality, the only thing they’re losing is water weight, which is temporary.

Katie, 27, tried her first teatox while prepping for her upcoming wedding, hoping to drop a few pounds before her big day.

“I follow several fitness people on Instagram, and I kept seeing it everywhere,” she explains. “Normally, I don’t go to the bathroom very often, and it’s super annoying, so I could tell a huge difference drinking the tea. I went every day, sometimes many times a day. I did almost poop my pants a couple of times, though. It just hits you and you have to go right away.”

Most of the teatoxes are sold in 7-, 14- or 28-day packs. Katie bought a 28-day pack, but confessed to taking a break from it every of couple days. “I wouldn’t drink any for a few days because I was going to the bathroom so often I didn’t want it to be too unhealthy, and then I’d start back again,” she says.

Haley, a friend of Katie’s, also decided to try a teatox and had a similar experience: “It woke me up out of my sleep with explosive [diarrhea] and painful cramping,” she recalls. “On a lighter note, though, I did feel instantly skinnier.”

While Katie managed to lose an impressive 10 pounds over the course of two months, she attributed much of her success to hardcore pre-wedding dieting and working out. And as with most fad diets, Katie admits she has since gained the weight back.

“It’s definitely not a long-term solution,” notes Wertheim. And there are health consequences: Over time, frequent diarrhea can cause electrolyte imbalances. In turn, this depletes potassium levels, which can cause abnormal heart rhythms.

Moreover, people who have abused laxatives may experience what’s called rebound constipation, meaning they have trouble going to the bathroom without the help of the laxative. If this still hasn’t dissuaded you from trying teatoxing, Wertheim doesn’t suggest doing it for more than a week or two max. Just be sure to stay hydrated—and don’t stray too far from the toilet.