What you’ll learn:
- Metformin is a trusted, affordable medication for type 2 diabetes that can also support weight loss and PCOS treatment off-label.
- Its most common side effects are digestive issues like diarrhea and nausea. They are typically temporary and can be minimized with gradual dosing, taking it with food, or switching to extended-release versions.
- Metformin works best when paired with healthy habits like regular movement, a balanced diet, and stress management.
Metformin is one of the most widely prescribed medications for type 2 diabetes and has been for decades. Although it was officially approved by the FDA in 1995, metformin’s roots go back even further, with its use beginning in parts of Europe as early as the 1950s. Today, it continues to be one of the most widely prescribed and trusted medications for helping people manage blood sugar, improve insulin sensitivity, and lower the risk of diabetes-related complications.
While it’s historically been prescribed for type 2 diabetes, metformin has also gained attention for its potential to support weight loss (off-label). It’s also often prescribed for polycystic ovary syndrome (PCOS) to help regulate cycles and improve fertility. Emerging research is also exploring its role in healthy aging and cancer prevention. While GLP-1 medications still show better weight loss results, metformin’s affordable price and long track record make it a compelling alternative for some people.
While metformin is well-tolerated by many, people tend to experience side effects, especially when starting the medication or after their dose is increased. Let’s walk through the most common side effects of metformin, the less common ones, some safety issues, and what you can do to minimize them.
How metformin affects your body
Metformin is an important medication for treating type 2 diabetes, but what does it actually do once it’s in your system? In simple terms, metformin helps your body use sugar more wisely—by making less of it, using it better, and releasing less of it at the wrong times. Here’s a closer look at how it does this in the body:
- It reduces glucose production in the liver – Metformin slows down the liver’s tendency to overproduce glucose in people with insulin resistance.
- It improves insulin sensitivity – Metformin also helps muscles and other tissues respond better to insulin, so cells can absorb and use glucose more efficiently.
- Lowers glucagon levels – Metformin helps prevent blood sugar spikes by reducing glucagon activity, a hormone that signals your liver to release stored glucose.
Metformin: How you take it and dosing
Metformin is taken as a pill, usually once or twice a day with meals, to help minimize stomach upset. There are two main types, each with unique benefits:
- Immediate-release (IR) – This form is typically taken two or three times per day. It may be a better option for people who need flexible dosing or a more immediate effect on blood sugar after meals.
- Extended-release (ER or XR) – This version releases the medication slowly over time, usually requiring just one daily dose. Many people find ER metformin easier to tolerate, with fewer side effects like nausea, gas, or cramping. It may also offer more stable blood sugar control throughout the day.
People typically start metformin at the lowest dose, 500 mg once a day, to give their body time to adjust. After about a week, if it’s well tolerated, the dose may be increased to 500 mg twice a day. From there, doctors may gradually raise the dose in weekly or biweekly steps, depending on how you respond and how you feel.
The maximum recommended dose is 2,500 mg per day, divided into two or three doses for immediate-release, or taken once daily with extended-release. This slow, step-by-step approach helps reduce common side effects like nausea, bloating, or diarrhea, and makes it more likely you’ll stick with the medication long term.
Metformin: Most common side effects
When you start metformin, your body may need time to adjust, especially your digestive system.
Gastrointestinal (GI) side effects are the most common reason people struggle with the medication at first. According to studies:
- Up to 25% of people experience some form of GI discomfort, including nausea, diarrhea, abdominal cramping, or gas, when they begin metformin.
- In about 5% of cases, the side effects are bothersome enough that people stop taking it altogether.
These symptoms often improve with time, especially if you start on a low dose and gradually increase. If immediate-release (IR) metformin continues to be hard on your system, you can talk to your doctor about switching to the extended-release (ER) version, which is absorbed more slowly and has been shown to cause fewer digestive side effects.
Here’s what you might experience:
- Diarrhea: This is the most commonly reported side effect of metformin.
- Nausea: It typically begins in the early days of treatment but tends to ease as your body adjusts to metformin.
- Stomach pain or cramping: These symptoms may occur, especially if metformin is taken on an empty stomach.
- Gas and bloating: These are common digestive side effects but are usually mild and temporary.
- Metallic taste in the mouth: While less common, some people report a metallic or bitter taste after taking metformin.
Taking metformin with meals, rather than on an empty stomach, and working with your provider to find the right dose and formulation can make a big difference in tolerability.
In clinical trials of Glucophage (a brand of metformin), digestive side effects were especially common with the IR version.
- Diarrhea affected 53% of people and led to medication discontinuation in 6% of them.
Other frequently reported issues included:
- Nausea and vomiting (25.5%)
- Flatulence (12%)
- Abdominal discomfort (6%).
Glucophage XR (extended-release metformin) showed a much lower side effect profile in similar trials. Only 9.6% of users reported diarrhea, and just 0.6% discontinued due to it. Nausea and vomiting were also significantly lower at 6.5%.
Side effects of stopping metformin
Stopping metformin can lead to a range of effects, depending on why you were taking it and how your body responds. Stopping metformin without transitioning to another treatment can cause any underlying issues to return.
Always consult your healthcare provider before making any changes—they can help monitor your blood sugar levels or recommend alternatives if necessary, and guide a safe and gradual taper if appropriate.
Here’s what you might experience:
- Increased blood sugar levels: Without metformin helping to control glucose production and improve insulin sensitivity, blood sugar can rise quickly in people with diabetes. Symptoms like increased thirst, frequent urination, fatigue, and blurred vision may appear. Over time, uncontrolled blood sugar can increase the risk of nerve damage, kidney problems, and heart disease.
- Return or worsening of underlying conditions: If you were using metformin for weight loss, PCOS, or insulin resistance, stopping it can cause symptoms to come back. People with PCOS might notice more irregular periods, acne, or weight gain.
- Changes in appetite and weight: You may notice that you feel hungrier and gradually regain weight after stopping metformin, and this is because the medication is actually helping suppress your appetite.
- Vitamin B12 concerns: Metformin can cause vitamin B12 deficiency over time. Even after stopping the drug, any existing deficiency won’t resolve immediately and might still need supplementation to manage symptoms like fatigue or numbness.
Are the metformin side effects different in females?
Yes—biological sex can influence how people respond to metformin, both in terms of side effects and metabolic benefits. Here’s what research shows:
For females:
- More likely to experience GI side effects: Women often report more frequent digestive symptoms like nausea, cramping, and diarrhea.
- Stronger metabolic response: Studies suggest women may see greater improvements in insulin sensitivity and glucose regulation.
- Potentially greater health benefits: When combined with lifestyle changes, women may also experience more significant reductions in markers like insulin levels or waist circumference.
For males:
- Fewer gastrointestinal issues: Men tend to report fewer digestive side effects than women.
Side effects and benefits can vary based on your biology. Your healthcare provider can help you personalize your dose and choose the right formulation—immediate-release (IR) or extended-release (ER)—to maximize results and minimize discomfort.
Metformin: Severe side effects and warnings
Metformin is usually well-tolerated and has a strong safety profile, but it can come with some rare but serious side effects:
- Lactic acidosis: This rare but serious condition can happen with metformin, affecting about 1 in 30,000 people. Signs include feeling extremely tired, muscle aches, shortness of breath, abdominal pain, or feeling unusually cold or dizzy. If you experience any of these, seek medical attention immediately.
- Allergic reactions to the medication are rare and may show up as itching, hives, or a rash. More serious signs include swelling of the face, lips, tongue, or throat, and trouble breathing. These symptoms require immediate medical care.
- Vitamin B12 deficiency can develop over time with long-term metformin use. According to research, metformin can cause a 5% increased risk of vitamin B12 deficiency in people with diabetes. Symptoms may include fatigue, numbness or tingling in your hands and feet, or difficulty concentrating. Routine blood tests can help your doctor monitor your B12 levels and recommend supplements if needed.
- Kidney problems are another important concern, especially since your kidneys play a key role in clearing metformin from your body. If your kidney function is impaired, metformin can build up and increase the risk of lactic acidosis. Be alert for symptoms like unusual swelling, reduced urination, fatigue, or shortness of breath.
If you ever experience symptoms that seem sudden or severe, go to the emergency room or call for immediate help.
Who shouldn’t take metformin?
While metformin can be helpful for many people, it’s not suitable for everyone. You should avoid taking it if you:
- Have serious kidney problems, or your kidneys aren’t working well
- Have liver disease
- Have recently had heart failure or a heart attack
- Have ever had lactic acidosis, especially if it was linked to metformin
- Are dehydrated or dealing with ongoing vomiting or diarrhea
- Are scheduled for a medical test or procedure that uses contrast dye (like a CT scan)—you may need to pause your dose for a short time
Also, make sure to let your provider know if you:
- Drink alcohol often or in large amounts—this can raise your risk of side effects
- Are pregnant or breastfeeding—metformin might still be an option, but only with close monitoring
- Take other medications that affect your kidneys or liver
Always talk to your healthcare provider before starting or stopping any medication. They can help you decide if metformin is safe and appropriate for your individual needs.
For more detailed safety information, visit the metformin safety page.
How to manage metformin side effects
Most of the side effects you’ll experience with metformin are manageable. In this section, we’ll walk through practical strategies that can help you feel better, stay consistent with your medication, and keep your health goals on track.
Medication adjustments that can reduce metformin side effects
How and when you take metformin can make a big difference in how well you tolerate it. Timing, dosage, and even the specific type of metformin all play a role in reducing side effects. These tips can help your body adjust more gently while keeping your treatment effective.
- Stick to a consistent schedule – Take your medication at the same time each day, ideally with your meals. This helps maintain steady levels in your system and minimizes surprises from side effects.
- Consider the extended-release version – If you’re dealing with persistent stomach issues, ask your doctor about extended-release (ER) metformin. It’s absorbed more slowly and is often easier on the gut, resulting in fewer gastrointestinal side effects.
If you’re still feeling unwell weeks after starting metformin, it’s worth revisiting your treatment plan. Sometimes, a different formulation or a slower dose increase is all it takes to feel better. Don’t hesitate to start this conversation—adjusting your dose is all part of the process.
Talk to your provider if:
- You’re skipping doses due to symptoms
- Digestive issues are disrupting daily life
- You’re noticing signs of low vitamin B12 (like fatigue or tingling)
- You’re unsure if your dose is too high or too low
How to eat to reduce metformin side effects
What you eat—and how you eat—can play a major role in how your body responds to metformin. Many of the common side effects, like diarrhea, can be improved with a few changes to your diet. Here’s how to adjust your food choices and eating habits to support your digestive system.
- Take it with food – Always take metformin with a meal or snack. Taking it with food not only helps reduce gastrointestinal side effects like nausea and cramping but also slows the medication’s absorption rate, which may improve tolerability and adherence. Studies show that taking metformin on an empty stomach is associated with a higher likelihood of nausea, abdominal discomfort, and diarrhea, especially during the initial dose adjustment phase.
- Eat smaller, more frequent meals – Try splitting your daily food intake into smaller, more frequent meals instead of a few large ones. This helps ease the digestive burden and may reduce bloating or diarrhea.
- Add more fiber – High-fiber foods can help regulate your digestion and ease symptoms. It’s best to increase fiber gradually to avoid worsening bloating or gas, especially if your body isn’t used to it. And always pair it with more water to help it move through your system smoothly.
- Stay hydrated – Metformin can sometimes lead to mild dehydration, especially if you’re experiencing diarrhea. Drink around 64 ounces of water per day, and more if you’re active or in hot weather.
Lifestyle modifications that can reduce metformin side effects
Metformin works best when paired with healthy lifestyle habits. Changes to your daily routine—like moving your body, getting enough sleep, and managing stress—can support your digestion and improve how your body processes the medication. Think of these tweaks as side-effect-reducing boosters to your overall wellness.
- Get moving – Regular physical activity helps improve insulin sensitivity and digestion. Aim for 20–30 minutes of walking, yoga, or light activity daily, and avoid intense exercise right after meals to reduce nausea.
- Prioritize sleep – Quality sleep helps your body recover and improves blood sugar control. Try sticking to a consistent bedtime and limiting screens before bed.
- Managing stress – Stress doesn’t just affect your mood—it can also raise blood sugar levels and make it harder for your body to respond well to metformin, especially in people with diabetes. Over time, chronic stress can impact sleep, digestion, and overall blood sugar control.
Comparing side effects: Metformin vs. GLP-1s
Metformin is typically used for diabetes and sometimes off-label for weight loss, like several GLP-1 medications. How are the side effects different? Let’s take a closer look at what you can expect and what the latest research says.
| Medication (dose) | Nausea/vomiting | Diarrhea | Key differences |
|---|---|---|---|
| Glucophage (Metformin ER) | 6.5% (combined) | 10% | Lowest rates of GI side effects overall |
| Glucophage (Metformin IR) | 25% (combined) | 53% | Highest rate of diarrhea; nausea comparable to some GLP-1s |
| Semaglutide (1.0 mg) – Ozempic® | 20%/9% | 9% | Higher nausea than metformin ER; diarrhea similar or lower |
| Semaglutide (2.4 mg) – Wegovy® | 44%/24% | 30% | Much higher rates of both nausea and diarrhea vs. metformin |
| Tirzepatide (15 mg) – Zepbound®/Mounjaro® | 28%/13% | 23% | GI side effects are more common than with either form of metformin |
| Liraglutide (1.8 mg)- Victoza® | 20%/9% | 12% | Nausea and diarrhea are slightly higher than with metformin ER |
| Liraglutide (3 mg) | 39%/16% | 21% | Higher GI side effects than both forms of metformin |
| Dulaglutide (4.5 mg) | 16%/9% | 11% | GI side effects are moderately higher than metformin ER |
Managing the side effects of metformin
Metformin remains a foundational medication in diabetes care, and it’s also used off-label to support weight loss, especially in people with insulin resistance or PCOS.
While newer GLP-1 receptor agonists like Wegovy® and Zepbound® may deliver stronger weight loss results, metformin offers a compelling option for those seeking a simpler, lower-cost, and well-tolerated alternative. By improving insulin sensitivity and reducing glucose production in the liver it helps regulate blood sugar while also supporting appetite control and, in some cases, modest weight reduction.
Metformin isn’t without side effects, though, especially during the first few weeks of treatment. Gastrointestinal discomfort is the most common issue, but for most people, these symptoms fade with time, proper dosing, and supportive habits like taking the medication with food.
Switching to an ER version can also improve tolerability. Work closely with your healthcare provider, stay mindful of how your body responds, and don’t hesitate to speak up if something doesn’t feel right. With the right adjustments, metformin can be a manageable and highly effective part of your long-term health and weight management plan.
At Noom, we’re here to help you make the transition smoother and more manageable. If you qualify for Noom Med, you’ll get personalized medication guidance, practical nutrition tips, and psychological support tailored to your medication experience. Whether it’s adjusting your meals to calm digestive issues or finding small ways to boost your energy, our team is here to help you feel your best.
