A muscle cramp is a strong, painful contraction or tightening of a muscle that comes on suddenly, lasting from a few seconds to several minutes. Soreness in the muscle may last for hours after the hard, tense cramp has stopped. Home treatment often relieves the pain.

The cause of muscle cramps is not always known. Muscle cramps may be brought on by many conditions or activities, such as:

• Exercising, injury, or overuse of muscles. A muscle that is very tired, not well-stretched, or held in poor posture may develop a cramp.
• Dehydration caused by exercising during hot weather often causes "exercise cramps" or "heat cramps." Muscle cramps can be caused by dehydration from vomiting, diarrhea, or not drinking enough fluids.
• Pregnancy. Cramps may occur because of decreased amounts of minerals such as calcium and magnesium, especially in the later months of pregnancy.
• Exposure to cold temperatures, especially to cold water.
• Other medical conditions, such as blood flow problems (peripheral arterial disease), kidney disease, thyroid disease, and multiple sclerosis.

Many medications can cause muscle cramps. If you suspect a medication is causing your leg problem:

• Call the health professional who prescribed the medication before taking another dose. The medication may need to be stopped, changed, or the dose adjusted. An appointment may not be necessary.
• If you are taking any medication not prescribed by a health professional, stop taking it. If you feel you need to continue taking the medication, call your health professional to discuss it.