Prediabetes means that your blood sugar is higher than it should be, but not high enough to be diabetes. Most people who get type 2 diabetes have prediabetes first.

Type 2 diabetes can have a big impact on your life. If you get it, you'll probably have to make some changes. For example, you may have to carefully watch what you eat, take medicine every day, and watch for other health problems.

Over time, diabetes can harm your eyes, nerves, and kidneys. It can damage your blood vessels. This can lead to heart disease, heart attack, and stroke. You could also have nerve damage. In your feet, this nerve damage can cause slow healing and pain when you walk. Your immune system may become weak and less able to fight infections.

The main way to prevent type 2 diabetes is to lower blood sugar with healthy lifestyle changes. The medicine metformin can also lower blood sugar.

Research shows that:

• For many people, making major lifestyle changes works better than taking metformin to help delay or prevent type 2 diabetes for up to 10 years.^{footnote 3, footnote 4} A follow-up study at 15 years showed that making major lifestyle changes was about equal to taking metformin in helping to delay or prevent type 2 diabetes.^{footnote 5}
• Making major lifestyle changes or taking metformin works very well to delay or prevent type 2 diabetes in:
  • People who have a BMI of 35 or more.^{footnote 3}
  • Women who have had gestational diabetes.^{footnote 1, footnote 6}
• Many people age 60 and older benefit more from making major lifestyle changes. And many people younger than 60 benefit more from taking metformin.^{footnote 7}

For some people, making major lifestyle changes or taking metformin can help delay or prevent type 2 diabetes for up to 15 years.^{footnote 5}

Some people may choose to take metformin and also make major lifestyle changes. Doing both of these things may give you the best chance of delaying or preventing type 2 diabetes over the long term.

You may be able to prevent or delay type 2 diabetes without taking medicine.

Studies show that making these three major lifestyle changes make getting type 2 diabetes less likely:^{footnote 3}

• Losing 7% or more of your weight, if you are overweight. If you weigh 200 pounds, losing 7% of your weight means losing 14 pounds.
• Getting at least 2½ hours (150 minutes) of moderate activity a week. Moderate activity gets your heart pumping. Examples are walking quickly, shooting baskets, and dancing.
• Eating a diet low in calories and saturated fat.

Some people may find it helpful to take part in a formal program like the National Diabetes Prevention Program to help them make these changes.

Lifestyle changes can:

• Help you lower blood sugar and prevent type 2 diabetes.
• Help control or prevent high blood pressure, high cholesterol, and heart disease.
• Help you feel better overall.

If you start slowly and follow your doctor's advice, there are few risks to making lifestyle changes. Some people do strain muscles or joints when they suddenly become active. But if you gradually increase how much activity you do, you're less likely to get hurt.

Sometimes the lifestyle changes are hard to keep up over time. If you stop doing them, you could raise your chances of getting type 2 diabetes.

Metformin:

• Can help you lower blood sugar and prevent type 2 diabetes.
• Is easy for some people to use. All you do is take medicine every day. But it is still important to make lifestyle changes if you can.
• Works very well and is generally safe.

Metformin has side effects. When some people first start taking metformin or start taking a larger dose, they feel sick to their stomach, have diarrhea or gas, or lose their appetite. These side effects usually go away after a short time. Or they can be avoided if the dose of metformin is increased slowly.

If you are breastfeeding or planning to get pregnant, you and your doctor can decide if taking metformin is the best decision for you. Metformin is probably safe for breastfeeding women and their babies. ^{footnote 2}

Metformin is also used to treat type 2 diabetes. Some people worry that taking metformin to prevent type 2 diabetes may mean that the medicine won't work as well if they get type 2 diabetes later on. But that's not true. Metformin will still work. You don't need to wait to take it.

People who made major lifestyle changes were compared with people who took metformin or a placebo and got information about lifestyle changes for type 2 diabetes.

*Based on the best available evidence (evidence quality: high)

Making major lifestyle changes or taking metformin both work better than a placebo pill at delaying or preventing type 2 diabetes. For many people, making major lifestyle changes works better than taking metformin to help delay or prevent type 2 diabetes for up to 10 years.^{footnote 3, footnote 4} A follow-up study at 15 years showed that making major lifestyle changes was about equal to taking metformin in helping to delay or prevent type 2 diabetes.^{footnote 5}

Let's compare people who made major lifestyle changes versus people who took metformin.^{footnote 3, footnote 8, footnote 5}

After 3 years:

• About 14 out of 100 people who made major lifestyle changes got type 2 diabetes. Compare that to about 22 out of 100 people who took metformin and got type 2 diabetes. That means 8 fewer people got type 2 diabetes after 3 years with lifestyle changes than with metformin.

After 10 years:

• About 27 out of 100 people who made major lifestyle changes got type 2 diabetes. Compare that to about 42 out of 100 people who took metformin and got type 2 diabetes. That means that 15 fewer people got type 2 diabetes after 10 years with lifestyle changes than with metformin.

After 15 years:

• About 55 out of 100 people who made major lifestyle changes got type 2 diabetes. Compare that to about 56 out of 100 people who took metformin and got type 2 diabetes. That means that 1 less person got type 2 diabetes after 15 years with lifestyle changes than with metformin.

These numbers apply to many people. But for some people, either making major lifestyle changes or taking metformin works very well to delay or prevent type 2 diabetes. This seems to be especially true for:

• People who have a BMI of 35 or more.^{footnote 3}
• Women who have had gestational diabetes.^{footnote 1, footnote 6}

Many people age 60 and older benefit more from making major lifestyle changes. And many people younger than 60 benefit more from taking metformin.^{footnote 7}

For some people, making major lifestyle changes or taking metformin can help delay or prevent type 2 diabetes for up to 15 years.^{footnote 5} But doing both of these things may give you the best chance of delaying or preventing type 2 diabetes over the long term.

*Based on the best available evidence (evidence quality: high)

Making major lifestyle changes or taking metformin both work better than a placebo pill at delaying or preventing type 2 diabetes in women who have had gestational diabetes for up to 3 years. But a follow-up study at 10 years showed that taking metformin works a little better than making major lifestyle changes in helping to delay or prevent type 2 diabetes.

Let's compare women who've had gestational diabetes who either made major lifestyle changes or who took metformin. ^{footnote 1 footnote 6}

After 3 years:

About 20 out of 100 women who made major lifestyle changes got type 2 diabetes. Compare that to about 22 out of 100 women who took metformin and got type 2 diabetes. That means 2 fewer women got type 2 diabetes after 3 years with lifestyle changes than with metformin.

After 10 years:

About 56 out of 100 women who made major lifestyle changes got type 2 diabetes. Compare that to about 51 out of 100 women who took metformin and got type 2 diabetes. That means 5 more women got type 2 diabetes after 10 years with lifestyle changes than with metformin.

Understanding the evidence

Some evidence is better than other evidence. Evidence comes from studies that look at how well treatments and tests work and how safe they are. For many reasons, some studies are more reliable than others. The better the evidence is—the higher its quality—the more we can trust it.

The information shown here is based on the best available evidence.^{footnote 3, footnote 8, footnote 5, footnote 1, footnote 6} The evidence is rated using four quality levels: high, moderate, borderline, and inconclusive.

Another thing to understand is that the evidence can't predict what's going to happen in your case. When evidence tells us that 2 out of 100 people who have a certain test or treatment may have a certain result and that 98 out of 100 may not, there's no way to know if you will be one of the 2 or one of the 98.

The American Diabetes Association (ADA) recommends making major lifestyle changes.

The ADA also suggests taking metformin, especially if you're younger than 60, have a body mass index (BMI) of 35 or more, or have had gestational diabetes.^{footnote 9}

The ADA recommends that you and your doctor talk about the benefits and risks of making lifestyle changes or using metformin to prevent type 2 diabetes and to make a decision based on your personal preferences and overall health.