Aleve is one brand of the over-the-counter drug naproxen sodium 220 milligrams (mg). It treats many types of mild pain. You may have taken it to treat your headaches, menstrual cramps, arthritis, muscles aches, toothaches, backaches, and even mild fever. If you take Aleve, though, you may wonder what else it does in your body.

Although Aleve can bring relief, it can also cause side effects. Some of these side effects can happen just from short-term use. Long-term use of Aleve can also cause other side effects. Some people are at greater risk of Aleve side effects because of certain medical conditions that they have.

Here’s what to know about how Aleve works and the side effects it can cause.

Aleve, or naproxen sodium 220 mg, is the over-the-counter version of naproxen sodium 275 mg, which is available by prescription only. Aleve is closely related to naproxen base 250 mg, also prescription only.

Both Aleve and its prescription counterparts belong to a class of medications called nonsteroidal anti-inflammatory drugs (NSAIDs). These drugs reduce pain and fever by preventing your body from making prostaglandins. Prostaglandins are substances your body produces when tissues of your body are injured. These substances contribute to many of the effects of inflammation, including swelling, fever, and pain.

Inhibiting your body’s production of prostaglandins can help prevent pain and other effects related to inflammation. But it can also interfere with some other functions.

Prostaglandins naturally help protect your stomach from damage. When Aleve reduces your prostaglandin production, it can cause:

These effects are more likely the older you are or the longer you use Aleve.

More serious side effects include:

  • swelling
  • bleeding
  • ulcers
  • tears in your stomach, small intestine, or large intestine

These effects can be fatal and can happen without warning. If you notice severe stomach pain or bloody or black, tarry stools while you take Aleve, stop taking the drug and call your doctor right away. To lower your risk of digestive system side effects, use the lowest effective dosage for the shortest time.

Aleve can also increase your blood pressure. You might not notice any signs that your blood pressure is increased. And if you already have high blood pressure, taking Aleve might make it worse. You should talk to your doctor before using Aleve if you have high blood pressure.

Aleve can also reduce your blood’s ability to clot. This can lead to bleeding. Talk to your doctor before using Aleve if you plan on having surgery soon.

Long-term use of Aleve can make your heart work harder. Aleve makes you retain water, which increases the load on your heart. This extra work can cause pressure on your cardiovascular system and can sometimes lead to a heart attack or stroke. These risks are even greater at higher dosages, even if you don’t have any heart conditions or risk of heart disease. Call 911 or local emergency services if you have:

  • chest pain
  • shortness of breath
  • slurred speech
  • weakness in your arms or legs

These are signs of a stroke or heart attack. If you take Aleve and have unexplained weight gain or swelling, especially in your legs and feet, talk to your doctor right away. These may be signs of heart failure. To lower your risk of heart problems, use the lowest dosage for the shortest amount of time.

Prostaglandins maintain the pressure in your kidneys so that these organs can filter the fluids in your body. A decrease in your level of prostaglandins from taking Aleve can cause problems with your kidney function. You may notice fluid retention or changes in how much you urinate. If you notice these changes while taking Aleve, stop taking it and contact your doctor.

People with certain medical conditions may experience more side effects from Aleve than other people. These conditions include:

If you have any of these conditions, talk to your doctor before using Aleve. Your doctor may suggest another medication to avoid complications.

For most people, Aleve is an effective treatment for mild pain and fever, especially for short-term use. Side effects can occur, but for the most part the effects are mild. Typically, more severe side effects are associated with extended use. But, as with any medication, if you have a medical condition, take other drugs, or simply aren’t sure if you should take it, talk to your doctor.