Researchers say metformin has the lowest adherence rate of any major diabetes drug. However, patients say there are ways to improve that percentage.

People who take the number one most commonly prescribed drug for diabetes are also the most likely to stop taking their medication.

Metformin works by reducing the amount of sugar released by the liver and improving how the body responds to insulin.

It’s been prescribed to more than 120 million people worldwide.

The drug’s lack of certain side effects compared to other medications are notable.

Metformin puts little if any strain on the organs, doesn’t cause weight gain, and comes with the added benefit of being the most affordable diabetes medication on the market.

It’s also sold under the brand name Glucophage, which costs significantly more.

However, the toll it takes on the digestive system may prevent many people with diabetes from taking it for more than a week or two.

“Metformin commonly causes gastrointestinal symptoms such as diarrhea and flatulence,” explained a recent study published in the journal Diabetes, Obesity and Metabolism.

The study was conducted by researchers from the University of Surrey.

The researchers examined the medication compliance rates of 1.6 million people with type 2 diabetes.

Metformin had the lowest adherence rate of the medications that were studied.

DPP-4 inhibitors — a class of oral diabetes medication that include the brand names Januvia and Tradjenta — appear to have the highest adherence rate. This class of drugs are also the most easily tolerated by the body, causing the least unpleasant side effects.

While some degree of metformin’s side effects can’t be helped, Marcey Robinson, MS, RD, CSSD, CDE, BC-ADM, co-founder of Achieve Health & Performance, says there are actually several things doctors can do when prescribing metformin to ensure patient adherence.

However, she says, many physicians simply don’t.

The first issue, Robinson told Healthline, is that there are two types of metformin to choose from: regular and extended release.

Most people do better on the extended-release version because the drug’s potency is affecting the body over the course of several hours, rather than hitting you all at once.

“Sometimes, it’s just a doctor’s standard of practice and they don’t even think about it. They’ve always prescribed it one way, so that’s what they continue to do,” said Robinson.

“For some patients, the doctor might also think that having a bigger boost of the medication all at once is going to help a patient who is struggling with high blood sugars after a meal. But that’s really not how metformin is expected to work in the body,” she added.

Gretchen Becker, author of “The First Year: Type 2 Diabetes: An Essential Guide for the Newly Diagnosed,” has been taking metformin for more than 20 years after receiving a diagnosis of type 2 diabetes in 1996.

“I never had any problems with metformin until I took a pill that I thought was the extended-release version, but it wasn’t,” Becker told Healthline.

Becker’s doctor had accidentally prescribed the regular form of metformin.

“I had very loose bowels for several months until I figured out what the problem was,” Becker said.

After getting the proper prescription, it took several months for Becker’s digestive system to recover.

Corinna Cornejo, who received a diagnosis of type 2 diabetes in 2009, told Healthline that her digestive woes didn’t start until she’d been taking metformin for more than a year.

“At first, I thought it was a response to dairy, but my doctor eventually switched my prescription to the extended-release version,” Cornejo recalled. “That has helped, but the side effect has not gone away completely.”

For some people, however, metformin’s unpleasant side effect of loose stools provides a much-needed balance to the side effects that can result from other diabetes drugs they’re taking.

“GLP-1 drugs, like Victoza or Byetta, can cause constipation,” explained Robinson. “Taking metformin with a GLP-1 drug means they actually complement each other, balancing out those side effects.”

And for some, metformin simply isn’t the right drug.

“No matter what you do, some patients just don’t tolerate the side effects well,” said Robinson.

Although there are many diabetes drugs on the market today, doctors will likely push metformin first.

“There has never been as many diabetes treatment options available as there are now,” explained Robinson. “But doctors look at cost, and metformin is the cheapest. Insurance companies tend to do that, too: ‘How can we pigeonhole everybody on this one drug?’ If you’re looking just from a cost perspective, you’re forcing people onto a drug regimen that simply doesn’t work for everyone.”

But there’s another pertinent reason Robinson believes so many people stop taking their diabetes medication: lack of education.

“If you look at the [American Diabetes Association] guidelines, the first line of defense is metformin, but there’s no education that is presented when the doctor prescribes it,” she said.

Robinson is the diabetes educator for Dr. David Borchers’ patients in Colorado.

“If the doctor didn’t have me to educate his patients, we’d have the same problem in this office with patients stopping their medication,” Robinson said. “Educators help ensure the patients understand why they’re taking that medication, and that leads to a much higher adherence rate.”

Teaching patients why they’re taking a certain medication, how to take it, and how it’s going to improve their health is key, insists Robinson. And it’s often overlooked.

For example, metformin should always be taken with food. The dose should be titrated at first, gradually increasing the dose over the course of several weeks, to prevent severe gastric distress.

This is a crucial detail that’s easily miscommunicated or misprescribed when patients don’t meet with a diabetes educator.

“I started taking metformin four years ago,” Tony Song, president and CEO of Diabetes Care Partners, told Healthline.

Song received a diagnosis of prediabetes in 2008.

“The first week was tough with diarrhea and a bit of dizziness. I started on a low dose, and I knew about this side effect, but I was surprised that my doctor did not mention any of this when I received the prescription,” he said.

Song contacted his doctor after the first week and was switched to the extended-release version. While it still caused diarrhea, it mostly resolved itself within two days.

If it weren’t for an in-depth understanding of how this medication was going to help his blood sugar, Song said the first week of side effects would’ve easily stopped him from continuing to take it.

And perhaps, added Song, there’s a degree of denial at play, too.

“Metformin is the first line of therapy for the newly diagnosed diabetic. It can be a hard pill to swallow, pun intended, because taking that pill is the action that states you now have diabetes,” he said.

Ginger Vieira is an expert patient living with type 1 diabetes, celiac disease, and fibromyalgia. Find her and her books on Diabetes Strong, and connect with her on Twitter and YouTube.