Metformin is most notorious for causing a wide array of stomach issues. “It varies from person to person, but up to 40 to 50 percent of people who use classic metformin can develop diarrhea, nausea, vomiting, and/or gassiness,” says Rodriguez.
One of the rarest side effects is lactic acidosis, a condition in which there’s an imbalance in the acid-base levels in your body. “This can present with muscle aches, pain, fatigue, chills, dizziness, drowsiness; very vague symptoms,” says Rodriguez.
It’s not uncommon for certain medications to leave you with an unpleasant, metallic taste in your mouth. “I've had a few patients tell me this—it’s difficult to explain why this happens, but it can occur,” says Rodriguez.
Metformin doesn't typically cause blood pressure to plummet and lead to hypoglycemia, but it can—and that can cause headaches. "Metformin alone should not cause hypoglycemia,” Rodriguez explains.
“One of the ways that people hypothesize metformin helps with weight loss is that, in some patients, it can help curb your appetite a little bit,” says Rodriguez. When your body’s insulin doesn’t respond normally, it can lead to cravings. Metformin can help stabilize insulin levels, thereby helping improve or curbing that sensation of extra hunger, she explains.