Can metformin cause hair loss? It is a question many patients ask after noticing increased shedding or thinning whilst taking this widely prescribed diabetes medicine. Metformin is a first-line treatment for type 2 diabetes in the UK and is also used off-label for conditions such as polycystic ovary syndrome (PCOS). Whilst it is natural to question whether a new medicine is responsible for changes you notice, hair loss is not listed as a recognised side effect of metformin in its UK-approved Summary of Product Characteristics. This article explores what the evidence actually shows, what else could be causing your hair loss, and when to seek medical advice.

Does Metformin Cause Hair Loss?

Hair loss is not a recognised side effect of metformin according to its UK-approved Summary of Product Characteristics, the NHS, or the EMA; any observed hair changes are more likely coincidental or related to the underlying condition being treated.

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Metformin is one of the most widely prescribed medicines in the UK, used primarily to manage type 2 diabetes. It is also used for conditions such as polycystic ovary syndrome (PCOS), although this use is off-label in the UK and should only be considered under medical supervision in line with NICE guidance (NG194). Given how commonly metformin is taken, it is natural for patients to question whether it could be responsible for changes they notice in their hair.

The short answer is that hair loss is not listed as a recognised side effect of metformin in the Summary of Product Characteristics (SmPC) approved for UK use (for example, the Glucophage SmPC available via the Electronic Medicines Compendium). The NHS Medicines A–Z and the European Medicines Agency (EMA) European Public Assessment Report (EPAR) for metformin similarly do not identify alopecia as a known adverse reaction. So, whilst the concern is understandable, there is no established regulatory link between metformin and hair loss based on current evidence.

That said, some patients do report noticing increased hair shedding or thinning after starting metformin. It is important to approach this carefully. Correlation does not equal causation — the timing of starting a new medicine and the onset of hair changes may be coincidental, or the hair loss may be related to the underlying condition being treated rather than the medicine itself. Understanding this distinction is key to finding the right explanation and, where necessary, the right solution.

If you believe metformin or any other medicine may be causing a side effect, you can report this to the MHRA via the Yellow Card scheme at www.mhra.gov.uk/yellowcard or through the Yellow Card app.

What the Evidence Says About Metformin and Hair Thinning

No large-scale clinical trials have identified hair thinning as a significant adverse effect of metformin; however, its well-documented reduction of vitamin B12 absorption may indirectly contribute to hair shedding in some long-term users.

When examining the scientific literature, the evidence linking metformin directly to hair loss remains weak and inconsistent. No large-scale, well-controlled clinical trials have identified hair thinning as a statistically significant adverse effect of metformin therapy. Spontaneous adverse drug reaction reports submitted to the MHRA's Yellow Card scheme do include occasional mentions of hair loss, but these reports are low in number and do not establish a causal relationship.

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One area worth noting is metformin's well-documented effect on vitamin B12 absorption. Long-term use of metformin can reduce the absorption of vitamin B12 from the gut by interfering with calcium-dependent uptake in the ileum. The MHRA Drug Safety Update (2022) on metformin and reduced vitamin B12 levels advises that B12 should be tested if a patient develops symptoms or signs of deficiency — such as anaemia, peripheral neuropathy, or glossitis — and that periodic monitoring should be considered in those at higher risk (for example, people who have taken metformin for a long duration or at high doses, those with dietary risk factors such as a vegan or vegetarian diet, or those with conditions affecting absorption). This is not a recommendation for routine periodic B12 testing in all long-term metformin users. NICE NG28 (Type 2 diabetes in adults: management) also acknowledges the risk of B12 depletion with long-term metformin use.

Vitamin B12 deficiency has been associated with telogen effluvium (diffuse hair shedding) in some reports, though the evidence for a direct causal link is mixed. It is therefore possible — but not established — that metformin-related B12 depletion could contribute to hair thinning in a small number of individuals over time. If you are concerned, speak to your GP rather than starting supplements independently, as testing before supplementation helps guide appropriate management and avoids masking a deficiency.

Metformin is also frequently prescribed to people with PCOS, a condition itself strongly associated with androgenetic alopecia (hormone-related hair thinning). In this context, it can be particularly difficult to separate the effects of the medication from those of the underlying hormonal condition. Research suggests that in women with PCOS, hair loss is more likely driven by elevated androgens than by metformin itself. Clinicians should therefore consider the full clinical picture before attributing hair changes to the medicine.

Other Causes of Hair Loss to Consider

Thyroid disorders, iron deficiency, androgenetic alopecia, and telogen effluvium are among the most common causes of hair loss and should be assessed before attributing shedding to metformin.

Before attributing hair loss to metformin, it is essential to consider the many other common and clinically significant causes of hair thinning. Hair loss is a multifactorial condition, and identifying the correct underlying cause is important for effective management.

Common causes of hair loss to consider include:

• Thyroid disorders — both hypothyroidism and hyperthyroidism can cause diffuse hair shedding; thyroid disease is common in the general population and is particularly associated with PCOS; assessment is warranted if clinically indicated

• Iron deficiency anaemia — low ferritin levels are a frequent and often overlooked cause of telogen effluvium (diffuse hair shedding)

• Vitamin B12 deficiency — as noted, metformin can reduce B12 absorption in some people, but dietary deficiency is also common, particularly in those following a vegan or vegetarian diet

• Vitamin D deficiency — low vitamin D has been associated with hair shedding in some studies, though the evidence is inconsistent; testing is recommended only when there are risk factors or clinical indications

• Androgenetic alopecia — the most common form of hair loss in both men and women, driven by genetic and hormonal factors

• Telogen effluvium — a temporary, diffuse shedding often triggered by illness, surgery, significant weight change, or emotional stress

• Autoimmune conditions — such as alopecia areata, which causes patchy hair loss

• Other medicines — several commonly prescribed drugs carry hair loss as a recognised side effect, including anticoagulants (such as warfarin and heparins), beta-blockers, retinoids, and statins; do not stop any prescribed medicine without first speaking to your GP or pharmacist

Given that type 2 diabetes and PCOS are both associated with metabolic and hormonal imbalances, patients taking metformin may already be at higher baseline risk of hair loss from these underlying conditions. A thorough clinical assessment is therefore far more informative than simply stopping the medication.

When to Speak to Your GP or Pharmacist

Consult your GP if hair loss is sudden, patchy, rapidly progressive, or accompanied by symptoms suggesting thyroid disease, B12 deficiency, or hormonal imbalance; do not stop metformin without medical advice.

If you have noticed increased hair shedding or thinning and are taking metformin, it is worth raising this with your GP or pharmacist — not because metformin is likely to blame, but because hair loss can sometimes signal an underlying condition that warrants investigation.

You should contact your GP if:

• Hair loss is sudden, patchy, or rapidly progressive

• You notice scalp redness, scaling, pain, or scarring at the site of hair loss, which may suggest a scarring (cicatricial) alopecia requiring prompt specialist assessment

• You are experiencing symptoms that may suggest a thyroid or hormonal problem, such as fatigue, unexplained weight changes, cold intolerance, or irregular periods

• You develop symptoms that could indicate vitamin B12 deficiency, such as tingling or numbness in the hands or feet, unusual tiredness, or a sore tongue

• You are a woman experiencing signs of virilisation — such as rapidly worsening hirsutism, a deepening voice, or other signs of excess androgens — which warrant urgent assessment

• Hair loss is causing significant distress or affecting your quality of life

• You suspect another medicine may be contributing

Your GP will decide which investigations are appropriate based on your history and examination. These may include a full blood count, ferritin, thyroid function tests, and vitamin B12, with additional tests such as hormone levels or vitamin D guided by your clinical picture rather than as a routine panel.

Your pharmacist can also provide useful guidance. They can review your full medication list for any drugs with hair loss listed as a known side effect, and advise on whether any supplements — such as B12 — might be appropriate after testing. Do not stop taking metformin without speaking to your GP first, as this medicine plays an important role in blood glucose management and stopping it abruptly could have consequences for your diabetes control.

Managing Hair Loss Whilst Taking Metformin

Treating any identified underlying cause — such as correcting B12 or iron deficiency — is the most effective approach; topical minoxidil is available over the counter for androgenetic alopecia, while persistent cases warrant dermatology referral.

If investigations reveal a specific deficiency or underlying condition contributing to hair loss, treating that cause is the most effective approach. For example, correcting a vitamin B12 deficiency — whether through oral supplementation or, in more severe cases, intramuscular injections — may help restore hair growth over several months. Similarly, addressing iron deficiency or optimising thyroid function can lead to meaningful improvement.

For those in whom no specific cause is identified, or where androgenetic or pattern hair loss is confirmed, several management options are available:

• Minoxidil (available over the counter in the UK) is a topical treatment licensed for androgenetic alopecia in both men and women; it works by prolonging the growth phase of the hair cycle. Before using minoxidil, read the Patient Information Leaflet carefully. It should be avoided during pregnancy and breastfeeding, and may cause initial increased shedding or scalp irritation in some people. Refer to the relevant SmPC (available via the Electronic Medicines Compendium) for full prescribing information.

• Finasteride is a prescription-only oral treatment licensed for androgenetic alopecia in men; it is contraindicated in women who are pregnant or may become pregnant due to the risk of harm to a male foetus.

• Anti-androgen treatments (for example, spironolactone) may be considered off-label for women with androgenetic alopecia under specialist supervision, with appropriate contraception and monitoring.

• Dietary support — ensuring adequate intake of protein, iron, zinc, and B vitamins through a balanced diet supports healthy hair growth.

• Stress management — since telogen effluvium is often stress-triggered, approaches such as mindfulness, regular exercise, and adequate sleep may be beneficial.

• Referral to a dermatologist — for persistent or complex cases, a specialist can offer further assessment and treatments. Platelet-rich plasma (PRP) therapy is sometimes discussed in this context, but current evidence for its benefit in hair loss is limited and it is not routinely commissioned on the NHS; any decision to pursue it should involve a detailed discussion with a specialist.

It is also worth noting that hair loss, whatever its cause, often improves with time. Telogen effluvium, in particular, tends to resolve spontaneously within six to twelve months once the triggering factor is addressed. Maintaining open communication with your healthcare team — and continuing metformin unless advised otherwise — remains the safest and most evidence-based approach. If you have concerns about your medication, always discuss them with a qualified healthcare professional rather than making changes independently. Suspected side effects can be reported to the MHRA via the Yellow Card scheme at www.mhra.gov.uk/yellowcard.

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