Metformin is one of the most widely prescribed drugs in the world. Millions of people with type 2 diabetes take it every day to keep their blood glucose (blood sugar) under control. For decades, metformin has been considered safe, reliable, and even protective against some other health problems in addition to diabetes. But in recent years, scientists have been asking another important question: Does metformin affect dementia risk?

Families affected by Alzheimer’s and other forms of dementia are eager to know the answer. If a common diabetes drug could either lower or raise the chances of developing memory loss, the impact would be huge. The truth is, the research is mixed — but new clinical trials are starting to paint a clearer picture.

What Is Metformin?

Metformin is a pill usually taken once or twice a day. It works by:

• Making the body more sensitive to insulin
• Helping the liver release less sugar into the blood

Doctors prescribe it mainly for type 2 diabetes, but sometimes also for conditions like polycystic ovary syndrome (PCOS). Because type 2 diabetes itself increases dementia risk, researchers want to know whether metformin helps protect the brain or could potentially harm it.

Dementia and Why It Matters

Dementia is not a single disease but a group of conditions that cause memory loss, difficulty thinking, and behavior changes. The most common type is Alzheimer’s disease, followed by vascular dementia, Lewy body dementia, and others.

People with diabetes are at higher risk of dementia. High blood sugar can damage small blood vessels in the brain, cause inflammation, and reduce the brain’s ability to use energy. Because metformin is the most common treatment for diabetes, it’s natural that scientists want to study whether it changes dementia risk.

Is Metformin Linked to Dementia? What Studies Show

The big question many people ask is: Is metformin linked to dementia? That answer is complicated because different studies have found different things.

Evidence Suggesting Protection

• A large review found that people with diabetes who took metformin had a lower risk of dementia than those who didn’t use it.
• In a study of nearly 400,000 people, metformin users had reduced rates of Alzheimer’s, Parkinson’s, and vascular dementia as long as it was before the onset of symptoms. The positive effects were most notable in people who had taken metformin long term.
• A systematic review and meta-analysis supported the evidence for a decreased risk of cognitive decline for those on metformin therapy with diabetes.
• Another study showed that a lower risk of dementia was associated with those on metformin versus those who were not on any treatment for diabetes, with longer-term use of metformin associated with an even lower risk.
• A case-control study found no evidence that using metformin increased the risk of Alzheimer’s disease, instead stating that long-term and high-dose metformin use was actually associated with a lower risk of Alzheimer’s disease.

These studies suggest that metformin might have protective effects on the brain, especially when used long term.

Evidence Suggesting No Effect or Mixed Benefits

Not all research points in the same direction:

• A 2025 systematic review and meta-analysis assessing dementia risk and metformin had mixed findings, with not enough evidence to support a definite answer.
• A 2023 study found that stopping metformin may actually raise dementia risk, suggesting that any protective effects may be lost if the drug is discontinued.

Because of these mixed results, scientists caution against making simple yes-or-no statements. Instead, they say metformin’s effects on dementia may depend on dose, length of use, and other health factors.

Can Metformin Cause Memory Loss?

Memory loss is not listed as a direct side effect of the drug, but there’s one important exception: Metformin can lower vitamin B12 levels if taken for many years.

A B12 deficiency can cause symptoms such as confusion, fatigue, and memory problems, which can also be called cognitive impairment. That means in rare cases, memory loss linked to metformin might actually be due to low B12, not the drug itself. This is why many doctors check B12 levels in long-term metformin users.

Can Metformin Cause Early-Onset Dementia?

Some people worry that metformin causes early-onset dementia. Early-onset dementia begins before age 65. So far, there is no evidence that metformin causes it. Most studies focus on older adults with diabetes. The main concern in younger people on metformin involves monitoring for vitamin B12 deficiency, not dementia risk.

Metformin and Dementia Lawsuits

You may see news stories or ads about lawsuits regarding metformin. In reality, lawsuits against metformin have mostly focused on contamination with NDMA, a possible cancer-causing chemical. These legal cases are about drug safety, not dementia. As of now, no lawsuit has proved that metformin directly causes Alzheimer’s or other types of dementia.

How Might Metformin Affect the Brain?

Researchers have several theories about why metformin might protect the brain — or in some cases, increase dementia risk. Here are possible ways metformin may protect the brain:

• Better blood sugar control — Improved blood sugar management prevents damage to small blood vessels in the brain.
• Reduced inflammation — Chronic inflammation is linked to Alzheimer’s disease, and metformin may lower inflammation.
• Increased insulin sensitivity — Increased insulin resistance in the body and brain can lead to a buildup of protein waste in the brain, which is known to damage brain tissue and is linked to dementia; metformin would help reduce the insulin resistance.

The primary way metformin could damage the brain is through vitamin B12 depletion. Long-term metformin use can lower B12, possibly leading to confusion or memory problems.

What Experts Say

Trusted health institutions, as well as the American Diabetes Association, recommend metformin as the first-line treatment for type 2 diabetes. Dementia is not considered a side effect. Instead, experts recommend:

• Staying on metformin if prescribed, unless your doctor advises otherwise
• Getting vitamin B12 levels checked every few years if you take metformin long term
• Telling your doctor right away if you notice new memory problems

Why This Research Matters

As the number of people living with dementia grows worldwide, understanding how common medications affect the brain is vital. Metformin is taken by millions of people every day. If it can help lower dementia risk, it could be an inexpensive and widely available tool for brain health. If metformin poses risks in some groups, that also needs to be understood.

For now, experts agree on this: If you take metformin, don’t stop without talking to your doctor. Managing diabetes well is one of the most powerful ways to protect both your body and your brain.

Join the Conversation

On myALZteam, people share their experiences with dementia, get advice, and find support from others who understand.

If you take metformin to manage your type 2 diabetes, have you noticed any differences in memory? Let others know in the comments below.