Does Metformin Give You Energy or Make You Tired?

Metformin isn’t a stimulant or a sedative, so how you feel on it depends on what it changes around your body’s energy rather than on any direct jolt or drain. Many people end up feeling more energetic once high blood sugar is under control. Others notice fatigue at particular times: early in treatment, years in, or during hard exercise. The question is usually less whether metformin causes tiredness and more which of a few traceable reasons is behind it.

How Metformin Can Leave You Feeling Better

High blood sugar itself causes tiredness, along with thirst and frequent urination, including trips to the bathroom at night. Lowering it with metformin can lift a fatigue you may have blamed on age or stress. Fewer nighttime bathroom trips may also mean better sleep, though that benefit is plausible rather than proven.

Metformin’s job is to lower the sugar your liver releases and help your muscles use sugar. Any gain in energy builds over weeks as blood sugar settles, not within an hour of a dose, so people expecting a buzz may wrongly conclude it isn’t working.

Feeling better usually looks modest: fewer afternoon slumps after meals, less thirst, fewer nighttime bathroom trips, and a more even mood through the day. Compare your energy with how you felt before treatment, not with yesterday, since day-to-day variation hides the trend.

Women with PCOS often report more energy too. In one group, the share reporting low energy and fatigue fell from 54% to 37% after metformin.¹ Women with PCOS taking metformin in a lifestyle program also felt more energetic and less fatigued, with better mood.² Metformin didn’t change body weight in that first group, so the energy gain wasn’t simply from weight loss.³

Metformin helps only if high blood sugar was part of your tiredness. If the fatigue comes from poor sleep, low mood or another condition, better control won’t fix it. If your readings or A1C improved but you still feel worn out, look for another cause.

Why Some People Feel Tired at First

Nausea and diarrhea are the most typical side effects, especially when starting.⁴ Poor sleep, dehydration and skipped meals from these effects can leave you drained. Metformin also tends to make people eat less, which can itself leave you low on energy.⁵

Doctors limit the early effects in a few ways. They usually start at 500 mg once or twice a day and raise the dose after 10 to 15 days.⁶ Taking it during or right after meals reduces stomach side effects.⁷ Extended-release tablets are designed to be gentler on the stomach, so ask about them if stomach trouble persists.

Early tiredness tends to track the stomach symptoms. It shows up on days with nausea or loose stools and eases on days without them, which helps you tie it to the drug. Tiredness with no stomach symptoms at all in the first weeks may have another cause and is worth mentioning to your doctor. A short log of dose times, meals, stomach symptoms and energy over two weeks gives your doctor something concrete to work from.

Your body may also be adjusting. If your sugar was very high, bringing it down quickly can feel tiring for a few weeks, and this usually fades as you adapt to normal levels. Fatigue that worsens after the first month deserves a call to your doctor.

Low blood sugar is a different cause. Metformin alone rarely drops sugar dangerously low, but combined with insulin or sulfonylureas such as glipizide, lows are more likely. Shakiness, sweating, sudden hunger or confusion suggest a low rather than ordinary tiredness, and a meter reading during the episode helps confirm it.

If diarrhea sets in, keep eating regular, plain meals so dehydration and an empty stomach don’t add to the fatigue. Don’t skip doses or stop on your own.

Low Vitamin B12 After Years on Metformin

People with type 2 diabetes taking metformin have lower vitamin B12 levels on average, pushing some into deficiency or borderline levels.⁸ Metformin interferes with a step your gut needs to absorb B12.⁹ Changes in gut movement and gut bacteria may further reduce absorption.¹⁰ The risk grows with years of use, which is why regular B12 checks are recommended.¹¹

Low B12 causes tiredness, weakness, pale skin and sometimes memory or mood changes. It can also damage nerves, causing numbness, tingling or burning in the feet that’s easy to mistake for diabetic nerve pain. In people on metformin for at least 4 years who had nerve damage, a daily 1 mg B12 tablet raised levels and improved pain, nerve function and quality of life.¹²

This tiredness creeps up. B12 falls slowly, so fatigue appears gradually over months or years, and people often blame age or diabetes instead. Correcting low B12 is usually straightforward, and metformin usually doesn’t need to be stopped.

Some people are more likely to run low. The longer you’ve taken metformin, the more likely your B12 has slipped, so someone on it for ten years has a higher chance than someone in their first year. Higher doses add to the chance. Older age, a vegan diet or acid-reducing medicines mean less reserve to begin with, so levels may fall sooner.

Reasonable reasons to ask for a test include persistent tiredness with no clear cause, tingling or numbness in the feet, or memory changes, especially after several years on metformin. Tingling feet can come from diabetes itself, so a B12 result helps separate a fixable cause from nerve damage that needs different management. A normal result is useful too, because it lets you and your doctor move on to other explanations.

The test is a simple blood draw, often added to routine diabetes bloodwork, and many doctors check yearly in long-term users. Borderline results may need a follow-up test for a clearer answer. Don’t start high-dose supplements before testing, since that can hide the diagnosis.

Mild or borderline low B12 is often handled with daily tablets, which can work even when absorption is impaired because a high dose lets some pass through. Injections are usually kept for severe deficiency, marked nerve symptoms, or tablets that fail to raise levels. After treatment starts, a repeat blood test confirms the level has come up. Fatigue often improves over weeks, though nerve symptoms can take longer. If you stay on metformin, the low B12 can return, so ongoing supplements or periodic rechecks are commonly needed.

Metformin and Exercise Energy

Metformin works partly by mildly slowing energy production in cells, especially in the liver.¹³ In short-term use it reduced peak aerobic fitness by about 3% and how long people could exercise by about 4%.¹⁴ Those effects are small enough that most people wouldn’t notice them in daily life.¹⁵ In amateur swimmers doing intervals, it changed lactate timing but not performance or effort felt.¹⁶

Most daily activity uses only a fraction of your maximum capacity, so a few percent off the ceiling rarely shows while climbing stairs or carrying shopping. People competing or training near their limit are the most likely to feel a difference, because they spend time at that ceiling.

If you train, hard intervals may feel slightly tougher or you may tire a bit sooner, while easy walks or gardening feel the same. Effects may vary with dose and how long you’ve taken it. Talk to your doctor before changing doses around workouts.

Training gains may also be smaller. In adults with high blood sugar who trained, those on metformin improved aerobic fitness by about 13% versus 25% without it.¹⁷ In older adults at risk of diabetes, metformin blunted the muscle energy improvements from 12 weeks of aerobic training.¹⁸ Exercise still improved fitness on metformin, so it’s always worth doing. Eat enough around workouts if your appetite is lower, and mention unusual breathlessness to your doctor.

Other Causes of Fatigue Worth Checking

Underactive thyroid causes tiredness and is common in people with diabetes. In people with an underactive thyroid, metformin lowers TSH, the main thyroid blood test number.¹⁹ It doesn’t change TSH in people with normal thyroid function.²⁰ If you take thyroid medicine, tell your doctor you’re on metformin when interpreting results.

Sleep apnea, depression, anemia and kidney problems all cause fatigue and are more common with diabetes. Blood sugar that stays high despite treatment keeps fatigue going too.

Simple blood tests can cover several suspects at once, including thyroid function, blood count for anemia, kidney function, B12 and blood sugar control. Snoring, waking unrefreshed or daytime sleepiness can flag sleep apnea, which is diagnosed with a sleep study rather than blood work. Low mood, loss of interest and poor concentration alongside tiredness suggest depression, which is treatable and worth raising openly. For an appointment, bring when the tiredness started relative to starting or changing metformin, your recent blood sugar readings, other symptoms like tingling, snoring or low mood, and a list of all medicines and supplements.

Extreme weakness with muscle pain, fast breathing or stomach pain can signal rare lactic acidosis. The risk is higher with kidney problems, heavy drinking or severe illness. Seek urgent care for these symptoms. Ordinary tiredness is not a reason to stop metformin on your own.