Metformin Myths and Facts: Tolerability, B12, and Long-Term Use

Metformin Is Still the Go-To Drug for Type 2 Diabetes - But People Keep Getting It Wrong

Metformin has been the first-choice medication for type 2 diabetes for over 25 years. It’s cheap, effective, and backed by decades of research. Yet, if you ask people on diabetes forums or social media what they think about it, you’ll hear the same complaints over and over: "It wrecked my stomach," "I got B12 deficiency," "I heard it’s dangerous long-term." The truth? Most of these are myths - or at least, they’re exaggerated. Let’s cut through the noise and look at what actually happens when you take metformin, especially over time.

Myth: Metformin Is Too Hard on the Stomach - Most People Can’t Handle It

It’s true that metformin can cause stomach issues. About 28% of people report diarrhea, nausea, or cramps when they first start taking it. That sounds bad, right? But here’s the part no one talks about: those symptoms usually fade. In the Diabetes Prevention Program Outcomes Study, which followed people for 15 years, GI side effects dropped to the same level as people taking a placebo after just the first year. Most people adapt.

Why do some struggle more than others? It’s often about how they start. Taking a full dose right away - say, 1000mg twice daily - is like throwing a rock into a calm pond. The ripples are big. But if you start with 500mg once a day with dinner and slowly increase by 500mg each week, the ripples barely ripple. A 2023 study showed this gentle ramp-up cut discontinuation rates from 15% down to just 5%.

And if you still can’t tolerate the regular version? Switch to extended-release (XR). It’s not magic, but it’s close. One chart review found that when patients switched from immediate-release to XR, diarrhea dropped from 18% to 8%. Abdominal pain fell by more than half. Many people who thought they were "allergic" to metformin just needed the right form.

Myth: Metformin Causes Lactic Acidosis - It’s Deadly and Common

Lactic acidosis sounds terrifying. And it’s listed in the warning label. But here’s the reality: you’re more likely to be struck by lightning than get lactic acidosis from metformin. The FDA estimates it happens in only 3 to 10 cases per 100,000 people each year. And almost all of those cases happen in people who have serious kidney or liver disease - conditions where metformin shouldn’t be used in the first place.

Metformin doesn’t cause lactic acidosis in healthy people. It doesn’t build up in your system if your kidneys are working normally. The fear comes from old studies in the 1970s, when a different biguanide (phenformin) was pulled from the market for this exact reason. Metformin is not phenformin. It’s safer. The DPP study tracked over 3,000 people for 15 years. Not one case of lactic acidosis occurred in the metformin group.

If you’re told to stop metformin because your creatinine is "a little high," ask for your eGFR. If it’s above 30, you’re probably fine. If it’s below 30, yes, you should stop. But that’s not a metformin problem - it’s a kidney problem.

Myth: Long-Term Use Damages Your Body - It’s Too Old to Be Safe

Metformin was first used in Europe in the 1950s. It’s been prescribed to millions since the 1990s. If it were secretly toxic over time, we’d know by now. The Diabetes Prevention Program followed people for 15 years. No hidden organ damage. No increased cancer risk. No mysterious decline in health.

What did change? A tiny dip in hemoglobin and hematocrit in the first year - then it stabilized. That’s not damage. That’s a mild, harmless effect on red blood cell production. It doesn’t cause anemia in healthy people. And it doesn’t get worse over time.

Weight? Metformin helps you lose 2-3% of your body weight - and you keep it off. Compare that to insulin or sulfonylureas, which make you gain weight. Metformin doesn’t just control blood sugar - it helps you stay leaner. That’s a long-term advantage most drugs don’t offer.

Fact: Metformin Can Lower Vitamin B12 Levels - And That’s Real

This is one myth that’s actually true. Long-term metformin use - usually over four years - can reduce vitamin B12 levels. A 2020 review found an average drop of 19% compared to people not taking it. Up to 30% of long-term users may develop low B12, especially if they’re older, vegetarian, or already at risk.

Why does this happen? Metformin interferes with how your gut absorbs B12. It doesn’t destroy it. It just makes it harder for your body to grab what you need from food or supplements.

What are the signs? Tingling in your hands or feet, fatigue, brain fog, or even anemia. These can be mistaken for aging or diabetes complications. But they’re treatable. If you’ve been on metformin for more than four years, get your B12 checked. It’s a simple blood test. If it’s low, your doctor can prescribe oral supplements - or even injections if needed. Most people bounce back fast.

The American Diabetes Association recommends checking B12 levels every 2-3 years if you’re on long-term metformin. The European Medicines Agency agrees. It’s not a reason to quit metformin. It’s just a reason to be smart about it.

Myth: Newer Diabetes Drugs Are Better - So Why Still Use Metformin?

Yes, newer drugs like GLP-1 agonists (Ozempic, Mounjaro) and SGLT2 inhibitors (Jardiance) have flashy benefits: weight loss, heart protection, kidney benefits. But they cost 10 to 20 times more. And they’re not always better for everyone.

Metformin still has the best long-term safety record. It’s been studied in more people, for longer, than any other diabetes drug. It doesn’t cause low blood sugar on its own. It doesn’t make you gain weight. It doesn’t need injections. And at $4-$10 a month, it’s the only drug that’s truly accessible to everyone.

The American Diabetes Association, the European Association for the Study of Diabetes, and the American College of Physicians all still say: start with metformin. Not because it’s the oldest. But because it’s the most proven.

That doesn’t mean you can’t add newer drugs later. Many people end up on metformin plus a GLP-1 agonist. But starting with the newer drugs? That’s like buying a sports car before you’ve learned to drive.

Real Stories: How People Actually Get Through Metformin

On Reddit, a user named Type2Warrior87 wrote: "Started on 500mg IR, had terrible diarrhea for 2 weeks. Doctor switched me to 500mg XR once daily with dinner - zero issues after 6 months." That’s the pattern. It’s not that metformin doesn’t cause problems. It’s that most problems can be fixed.

Another person on Diabetes Daily said: "I took it with food, slowed the dose, and now I’ve been on it for 8 years with no side effects. It’s the only thing keeping my A1C under 6.5."

But not everyone adapts. About 4% of people still quit because of side effects. If you’re one of them, don’t feel like a failure. Talk to your doctor. Try XR. Try a lower dose. Try taking it with a bigger meal. There’s almost always a workaround.

One Healthgrades review said: "XR worked for 3 months, then nausea came back. Had to stop." That’s rare, but it happens. For those people, other options exist. But for the vast majority? Metformin still works.

How to Take Metformin Right - The Practical Guide

• Start low: 500mg once daily with your evening meal.
• Go slow: Increase by 500mg every week until you reach your target dose (usually 1000-2000mg daily).
• Switch to XR: If GI issues persist, ask for the extended-release version. Once daily at bedtime often works best.
• Take with food: Even if you’re on XR, food helps reduce stomach upset.
• Check B12: After 4 years of use, get your B12 levels tested every 2-3 years.
• Don’t panic over creatinine: If your eGFR is above 30, you’re likely fine. Ask for the number, not just "your kidney numbers are off."

Final Thought: Metformin Isn’t Perfect - But It’s Still the Best Starting Point

It’s not a miracle drug. It doesn’t fix everything. It can cause stomach issues. It can lower B12. But it’s the only diabetes medication that’s been proven to help you live longer, stay leaner, and avoid complications - all for less than $10 a month.

The myths around metformin aren’t just wrong - they’re dangerous. People stop taking it because they think it’s unsafe. But the real danger? Letting your blood sugar run high for years because you’re afraid of a pill that’s saved millions.

Metformin isn’t perfect. But it’s the closest thing we have to a foundation. Build your treatment on it. Then add other tools if you need them. Don’t throw it away because of a myth.