Does metformin cause hair loss or thinning?
Metformin does not directly cause hair loss based on current clinical evidence, though there are isolated anecdotal reports. Hair loss in metformin users is more likely related to underlying conditions such as vitamin B12 deficiency from long-term use, diabetes-related complications, or other health factors rather than the medication itself.
Interestingly, research shows metformin may actually improve hair growth in certain conditions, particularly in women with polycystic ovary syndrome (PCOS). In this article, we’ll review current evidence of the effects of metformin on hair loss.
Is Hair Loss a Documented Side Effect of Metformin?
Hair loss is not listed as a recognized adverse effect in FDA prescribing information or official drug labels for metformin. The most commonly documented side effects include gastrointestinal issues (nausea, diarrhea, abdominal pain), vitamin B12 deficiency with prolonged use, and rarely, lactic acidosis.
A comprehensive pharmacovigilance study analyzing over 10.5 million case reports from the FDA Adverse Event Reporting System found 56,674 adverse events related to metformin, with the most significant safety signals involving metabolic and gastrointestinal disorders rather than hair loss.
Clinical trials spanning decades have failed to establish a direct causal relationship between metformin and alopecia (hair loss). In fact, some research suggests metformin may actually promote hair growth in certain conditions. A 2002 study of 16 women with PCOS and hirsutism found that metformin treatment significantly improved hair growth parameters compared to placebo.
Possible Mechanisms Behind Hair Loss
While metformin does not directly cause hair loss, several indirect pathways may contribute to hair thinning in some users. Unlike medications that directly disrupt hair follicle cycling or cause immediate follicular damage, metformin's potential association with hair loss primarily occurs through secondary effects on nutritional status, metabolic function, and underlying health conditions.
Vitamin B12 Deficiency
The most scientifically supported indirect mechanism linking metformin to hair loss involves vitamin B12 deficiency. Long-term metformin use can impair vitamin B12 absorption through interference with the calcium-dependent binding of the vitamin B12-intrinsic factor complex to receptors in the terminal ileum.
Vitamin B12 deficiency may contribute to hair loss through different possible mechanisms:
- Reduced oxygen delivery to hair follicles due to impaired red blood cell production
- Disrupted cell division essential for hair growth
Studies show a dose and duration-dependent relationship between metformin use and B12 deficiency, which means taking a higher dose of metformin may put you at a higher risk of low B12 levels.
Diabetes or Blood Sugar Fluctuations
Uncontrolled diabetes itself may cause telogen effluvium, a temporary form of hair loss where hair follicles prematurely enter the resting phase. More research is needed to prove causation and determine the mechanism behind hair loss caused by high blood sugar levels or insulin resistance.
A case report documented telogen effluvium occurring 2-3 months after treatment of diabetic ketoacidosis, highlighting how metabolic stress from blood sugar fluctuations might trigger hair loss.
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Other Contributing Factors
Additional factors that may contribute to hair loss in metformin users include:
- Thyroid disorders
- Chronic stress from managing a long-term condition
- Nutritional deficiencies beyond B12
- Concurrent medications
Who is At-Risk for Hair Loss During Metformin Treatment?
Older adults face the highest risk of hair loss during metformin therapy, with institutionalized elderly residents showing a 53.2% prevalence of B12 deficiency when taking metformin compared to 31% in diabetic patients not taking metformin. Age itself is an independent risk factor, with each 10-year age increment conferring a 1.36-fold increased risk.
Other individuals that may be at a higher risk of hair loss include:
- Women with PCOS or going through menopause
- Patients with dietary restrictions or gastrointestinal (GI) disorders
- Those oversupplementing with certain nutrients
- Patients with a history of COVID-19 infection
- Individuals identified as obese
Speak with your healthcare provider about your risk factors for hair loss, and ways to improve your hair health.
How to Manage Hair Loss While on Metformin
Healthcare providers should monitor vitamin B12 levels in metformin users, particularly those at higher risk. Treatment options for low vitamin B12 include oral or injectable B12 supplementation. Do not take supplements, including vitamin B12, without first consulting with a healthcare professional.
If you experience hair thinning while taking metformin, contact your healthcare provider for an evaluation. They can help you find out the cause and recommend appropriate treatment options.
When to See a Doctor
Patients should seek medical attention for:
- Rapid or patchy hair loss: Sudden hair loss or loss in circular/patchy patterns may indicate alopecia areata or other autoimmune conditions.
- Excessive daily hair shedding
- Visible scalp changes including redness, scaling, or inflammation
- Neurological or systemic symptoms, including: Extreme fatigue and weakness, pins and needles, numbness
- Cognitive changes or memory problems
Always consult a healthcare provider before discontinuing or switching diabetes medications, as the benefits of metformin in diabetes management typically outweigh potential risks. Alternative diabetes medications may have their own side effect profiles and may not provide equivalent metabolic benefits.
This is not all the information you need to know about metformin for safe and effective use and does not take the place of your doctor’s directions. Review the full patient medication guide and discuss this information and any questions you have with your doctor or other health care provider.
References
- Almohanna, H. M., Ahmed, A. A., Tsatalis, J. P., & Tosti, A. (2019). The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatology and therapy, 9(1), 51–70. https://doi.org/10.1007/s13555-018-0278-6
- American Academy of Dermatology Association. (2024, August 6). Can COVID-19 cause hair loss? American Academy of Dermatology. Accessed on August 28, 2025 at https://www.aad.org/public/diseases/hair-loss/causes/covid-19
- Atkinson, M., Gharti, P., & Min, T. (2024). Metformin Use and Vitamin B12 Deficiency in People with Type 2 Diabetes. What Are the Risk Factors? A Mini-systematic Review. TouchREVIEWS in endocrinology, 20(2), 42–53. https://doi.org/10.17925/EE.2024.20.2.7
- Coogan, P. F., Bethea, T. N., Cozier, Y. C., Bertrand, K. A., Palmer, J. R., Rosenberg, L., & Lenzy, Y. (2019). Association of type 2 diabetes with central-scalp hair loss in a large cohort study of African American women. International journal of women's dermatology, 5(4), 261–266. https://doi.org/10.1016/j.ijwd.2019.05.010
- Du, Y., Zhu, J., Guo, Z., Wang, Z., Wang, Y., Hu, M., Zhang, L., Yang, Y., Wang, J., Huang, Y., Huang, P., Chen, M., Chen, B., & Yang, C. (2024). Metformin adverse event profile: a pharmacovigilance study based on the FDA Adverse Event Reporting System (FAERS) from 2004 to 2022. Expert review of clinical pharmacology, 17(2), 189–201. https://doi.org/10.1080/17512433.2024.2306223
- Guo, E. L., & Katta, R. (2017). Diet and hair loss: effects of nutrient deficiency and supplement use. Dermatology practical & conceptual, 7(1), 1–10. https://doi.org/10.5826/dpc.0701a01
- Kelly, C. J., & Gordon, D. (2002). The effect of metformin on hirsutism in polycystic ovary syndrome. European journal of endocrinology, 147(2), 217–221. https://doi.org/10.1530/eje.0.1470217
- Kim, J., Ahn, C. W., Fang, S., Lee, H. S., & Park, J. S. (2019). Association between metformin dose and vitamin B12 deficiency in patients with type 2 diabetes. Medicine, 98(46), e17918. https://doi.org/10.1097/MD.0000000000017918
- Metformin [package insert]. Updated February 2025. TIME CAP LABORATORIES, INC. Accessed on August 27, 2025 at https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=542cec22-eeae-4704-9bb6-4176640e5ea8
- Owecka, B., Tomaszewska, A., Dobrzeniecki, K., & Owecki, M. (2024). The Hormonal Background of Hair Loss in Non-Scarring Alopecias. Biomedicines, 12(3), 513. https://doi.org/10.3390/biomedicines12030513
- Prasad, S., De Souza, B., Burns, L. J., Lippincott, M., & Senna, M. M. (2020). Polycystic ovary syndrome in patients with hair thinning. Journal of the American Academy of Dermatology, 83(1), 260–261. https://doi.org/10.1016/j.jaad.2020.01.075
- Succurro, E., Palleria, C., Ruffo, M., Serra, R., Arturi, F., & Gallelli, L. (2017). Loss of Eyebrows and Eyelashes During Concomitant Treatment with Sitagliptin and Metformin. Current drug safety, 12(1), 10–12. https://doi.org/10.2174/1574886311666161014125536
- Smolarczyk, K., Meczekalski, B., Rudnicka, E., Suchta, K., & Szeliga, A. (2024). Association of Obesity and Bariatric Surgery on Hair Health. Medicina (Kaunas, Lithuania), 60(2), 325. https://doi.org/10.3390/medicina60020325
- Ting, R.Z., et. al. Risk Factors of Vitamin B12 Deficiency in Patients Receiving Metformin. Arch Intern Med. 2006;166(18):1975–1979. DOI: https://doi.org/10.1001/archinte.166.18.1975
- U.S. Food and Drug Administration. (2023, December 7). FDA Adverse Event Reporting System (FAERS) Public Dashboard. U.S. Food and Drug Administration. Retrieved from https://www.fda.gov/drugs/fdas-adverse-event-reporting-system-faers/fda-adverse-event-reporting-system-faers-public-dashboard
- Wong, C. W., Leung, C. S., Leung, C. P., & Cheng, J. N. (2018). Association of metformin use with vitamin B12 deficiency in the institutionalized elderly. Archives of gerontology and geriatrics, 79, 57–62. https://doi.org/10.1016/j.archger.2018.07.019
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