People are using a 20-cent diabetes drug to lose weight and reverse aging — but it can cause explosive diarrhea

• Metformin is a diabetes drug that's also taken off-label for weight loss and anti-aging.
• It can have some severe gastrointestinal side effects, including diarrhea without warning.

It started out like any other last-minute trip to the grocery store. Dressed in pants, a top, and a colorful shawl draped around her shoulders, Gina Holden headed into the supermarket, grabbed what she needed, and hustled back to her car.

It was 2016, and Holden, then in her mid-60s, had been on metformin for about 18 months to control her type 2 diabetes. At the time she was diagnosed, a doctor told her it was the best medicine around for her condition.

Over the course of the year and a half since she started taking metformin, she had already dealt with the gastrointestinal side effects of the medication many times, including some recurring episodes of violent diarrhea. But nothing had prepared her for what was coming next.

As Holden placed the groceries in her car, suddenly, she knew she needed to find a bathroom. Immediately.

"By the time I got into the store and in the stall in the bathroom, everything just let loose — it just flowed all over the floor," she told Insider.

After cleaning herself up, Gina had to devise a way to get out of the store with no clean pants and no clean underwear.

"I tied the shawl around me, held my head up high and walked to the car," she said.

Metformin 'can really upset your system,' patients say

Holden shared her story with Insider willingly, even though she admits it is embarrassing, gross, and — now that it's all over — something "we all laugh about." She shared it because she said she's "flabbergasted" and concerned that people would use the same diabetes drug that caused her so much grief for off-label purposes like anti-aging and weight loss.

Metformin is a cheap, generic, metabolism-changing drug that's available without a prescription in many countries. The World Health Organization considers the pill an "essential" must-have for pharmacies worldwide, because of how well it regulates blood sugar for diabetic and pre-diabetic people. It's also increasingly being used off-label for weight loss, or to potentially delay aging in older adults. Yet a percentage of people who try metformin, anywhere from one tenth to one third of patients, may never tolerate this medication well.

It's true that many people lose a few pounds when they start metformin — one study found the average is about six pounds.

But "do they know the side effects?" Holden said. "It can really upset your system."

Other patients who'd been on metformin for as long as 20 years told Insider that suddenly, they too developed severe, floodgate-style diarrhea like Holden's. The kind that led to embarrassing episodes at restaurants, casinos, and family gatherings. These patients requested to only be identified by their first names, because the episodes were so shameful and isolating. The patients that Insider spoke to were all over the age of 65, but none had had incontinence issues before taking metformin.

Doctors caution that it's difficult to blame metformin single-handedly for these events, or to know for sure the diabetes pill was the cause of these accidents. However the patients Insider spoke to said that all of the embarrassing diarrhea issues ceased once they stopped taking metformin.

One patient had diarrhea so severe she had to be hospitalized

Richard, age 78, had been on metformin for about 20 years for his type 2 diabetes when the severe diarrhea episodes started happening. At first, he rationalized the accidents: Maybe he got food poisoning. Maybe the eggs weren't fully cooked.

Finally, when he "just couldn't make it to the bathroom" one time and there wasn't a clear culprit involved, he decided to talk to his doctor.

A colonoscopy came back clean. But, one of his doctors suggested he come off metformin, just to see if it helped his condition. As soon as Richard quit metformin, and started eating some some probiotic yogurt every day, his GI issues went away.

"I will say that my stomach, my whole gut is off-base and to this day it still continues to be a little bit of a issue, but at least it's allowing me time to get to the bathroom," he said.

84-year-old Irma shared a similar experience with Insider. She had been taking a low dose of metformin without issue for about three or four years when, over the course of a few months in the fall of 2021, diarrhea became part of her daily life.

"Most of the time I didn't make it to the bathroom," she told Insider, saying she "had very little warning."

Irma started taking over the counter stomach remedies like Pepto Bismol, but they didn't seem to help much. In fact, the diarrhea was getting worse, and so was Irma.

Over the course of about a week, she became so severely dehydrated that she finally called 9-1-1 and had to be rushed to the hospital.

At the hospital, doctors suggested that the metformin might've been a key factor at play in the severe diarrhea. So, Irma went off the medication, and started taking another diabetes drug instead. She says diarrhea hasn't been an issue.

"Never before, and never since," she said.

Doctors say there are several things patients can do lessen the risk of an embarrassing 'episode'

Most doctors suggest starting metformin at a smaller dose, and ramping up to a higher prescription strength.

"You really do need to titrate up slowly," Dr. Susan Spratt, a metabolism specialist and endocrinologist at Duke University Hospital, told Insider. "Sometimes, people cannot tolerate the maximum dose and we just try to get them on the maximum tolerated dose."

Dr. Nir Barzilai, who is currently on a yearslong quest to investigate whether metformin really can slow down aging, says that there are some people who won't ever be able to tolerate the drug, and part of that may come down to genetics.

For the first week or so, most metformin patients might experience an upset stomach, cramps, feeling full with very little food, and some diarrhea.

"It usually goes away, except in some people it doesn't go away," Barzilai told Insider. "And then they shouldn't be on metformin."

Metformin intolerance might also be influenced by environmental factors, including your diet, so it can help to limit simple carbs like white bread, white rice, and sweet treats, Spratt suggested.

Finally, it can be worth trying extended release versions of metformin, which are more expensive, but tend to come with fewer stomach-turning side effects, because they are released more slowly in the gut.

"Besides the GI side effects, it is a pretty benign drug to take," Spratt said.

Despite its off-label popularity, metformin is not recommended by doctors for young, healthy people without metabolic issues. Dr. Barzilai warns "young people, less than 50 or 40" that the drug can be "harmful" for them, because it can have a detrimental effect on testosterone, on muscle building, on sperm, and, in rare cases, on liver function.