Does metformin make you tired?
Does metformin make you tired? It can, usually from low blood sugar, GI upset, or B12 deficiency. Here is what to watch for and when to call.
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Does metformin make you tired? It can, but fatigue is not one of the most common reasons people stop metformin. When tiredness happens, it is often related to low blood sugar (especially with other diabetes medicines), stomach side effects that reduce eating, or vitamin B12 deficiency over time. This guide explains the most likely reasons and what to watch for so you can discuss next steps with a clinician.
- Yes, metformin can make you tired, but it is not inevitable and often has a fixable cause.
- Tiredness may come from low blood sugar, stomach side effects, or dehydration from diarrhea.
- Long-term metformin use can lower vitamin B12, which can contribute to fatigue and nerve symptoms.
- Call a clinician urgently for severe weakness with fast breathing, vomiting, or worsening confusion.
Answer: can metformin cause tiredness?
Why you might feel tired on metformin
Low blood sugar (hypoglycemia)
Metformin by itself is less likely to cause low blood sugar, but the risk can rise if you also use insulin or medicines that increase insulin release. Low blood sugar can feel like sudden fatigue, shakiness, sweating, hunger, headache, or confusion. A clinician can help you review your medication list and glucose patterns.
Nausea or reduced appetite
Nausea, stomach upset, and reduced appetite can make you eat less than usual, which can leave you feeling drained. These effects are described in prescribing information and are often most noticeable early in treatment or after dose changes. Tell your clinician if fatigue tracks with poor intake or nausea.
Diarrhea and dehydration
Diarrhea is a common metformin side effect and can lead to dehydration or electrolyte imbalance, which may feel like weakness or tiredness. If you have persistent diarrhea, dizziness, fainting, or you cannot keep fluids down, contact a clinician promptly. Do not ignore fatigue that comes with signs of dehydration.
Vitamin B12 deficiency over time
Metformin can reduce vitamin B12 absorption, and the FDA label advises that B12 levels should be checked periodically in patients on metformin. Low B12 can cause fatigue and may also cause numbness or tingling in hands or feet. A clinician can interpret your B12 result and decide whether supplementation or further testing is needed.
Lactic acidosis warning symptoms
Metformin carries a boxed warning for lactic acidosis, a rare but serious condition. Symptoms can include unusual tiredness or weakness along with other red flags such as trouble breathing, stomach pain, nausea or vomiting, dizziness, or feeling cold. Seek urgent medical care if these occur.
| What you notice | Possible reason | What to discuss with a clinician |
|---|---|---|
| Fatigue with shakiness, sweating, confusion | Low blood sugar, especially with insulin or sulfonylureas | Medication interactions, glucose logs, and whether labs or monitoring are needed |
| Fatigue after meals are skipped due to nausea | GI side effects leading to low intake | Whether extended-release metformin or slower titration is appropriate |
| Fatigue with frequent diarrhea or lightheadedness | Dehydration or electrolyte imbalance | Hydration status, severity, and whether other causes should be ruled out |
| Gradual fatigue plus numbness or tingling | Vitamin B12 deficiency | Checking B12 periodically and addressing deficiency if present |
| Severe weakness plus fast breathing or persistent vomiting | Possible lactic acidosis or another emergency | Urgent evaluation rather than waiting for routine follow-up |
When to talk to a clinician about fatigue
Get urgent care for red flags
Seek urgent medical care for severe weakness or unusual tiredness with trouble breathing, persistent vomiting, severe abdominal pain, confusion, dizziness or fainting, or feeling very cold. These can be warning signs of lactic acidosis or another serious problem that needs immediate evaluation.
Call soon if fatigue is persistent
If tiredness lasts more than a few days, interferes with work or daily life, or is getting worse, contact your clinician. Bring a list of all medications and supplements, and note whether symptoms track with meals, diarrhea, or sleep changes. This helps identify whether metformin is the likely driver or a contributor.
Ask about B12 testing
If you have ongoing fatigue, anemia, or numbness or tingling, ask whether checking vitamin B12 makes sense. The metformin label notes that B12 levels should be checked periodically in patients taking metformin. Your clinician can decide what interval is appropriate for you.
Discuss other causes too
Fatigue has many possible causes, including thyroid disease, iron deficiency, sleep apnea, depression, and uncontrolled blood sugar. If your clinician thinks metformin is not the main cause, they may recommend targeted labs or evaluation based on your symptoms and history.
Practical tips that may help
Track timing and triggers
Note when fatigue starts, meal timing, and any GI symptoms to share with your clinician.
Review all medications
Ask whether other diabetes drugs raise low blood sugar risk when combined with metformin.
Do not ignore diarrhea
Persistent diarrhea can cause dehydration and fatigue. Contact a clinician if it continues.
Consider B12 if symptoms fit
Fatigue with tingling or numbness can point to B12 deficiency, which metformin can worsen.
Use labs to guide decisions
A1c and glucose patterns and B12 status can clarify what is driving fatigue.
Frequently Asked Questions
Does metformin make you tired at first?
It can, especially early on if nausea or diarrhea reduces how much you eat or drink. If fatigue is severe, persistent, or comes with warning symptoms like trouble breathing or repeated vomiting, seek urgent evaluation.
Can metformin cause low blood sugar and make you feel weak?
Metformin alone is less likely to cause low blood sugar, but the risk can increase when it is used with insulin or medicines that increase insulin release. Low blood sugar can feel like weakness, shakiness, sweating, or confusion, and should be discussed with a clinician.
Can metformin make you tired by lowering vitamin B12?
Yes. The FDA label notes that metformin can lower vitamin B12 levels and recommends periodic monitoring. If you have fatigue, anemia, or numbness or tingling, ask a clinician whether B12 testing is appropriate.
When is tiredness on metformin an emergency?
Get urgent care if unusual tiredness or weakness happens with trouble breathing, severe stomach symptoms, dizziness or fainting, confusion, or feeling cold. These can be warning signs of lactic acidosis or another serious condition that needs immediate evaluation.
What labs can help figure out why I am tired on metformin?
A clinician may review glucose measures such as A1c and blood glucose to look for patterns that could contribute to fatigue. Because metformin can lower vitamin B12 over time, B12 testing may also be considered based on your symptoms and history.