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Muscle Cramps

By Michael C. Levin, MD, University of Tennessee Health Science Center

A cramp is a sudden, brief, unintended (involuntary), and usually painful contraction of a muscle or group of muscles.


The most common causes of muscle cramps are

  • Benign leg cramps that occur for no known reason, typically at night

  • Exercise-associated muscle cramping (cramping during or immediately after exercise)

Muscle cramps (also called charley horses) often occur in healthy people, usually in middle-aged and older people but sometimes in younger people. Cramps tend to occur during or after vigorous exercise but sometimes occur during rest. Some people have leg cramps during sleep. These painful cramps usually affect the calf and foot muscles, causing the foot and toes to curl downward. Although painful, these cramps are usually not serious and are thus called benign leg cramps.

Having tight calf muscles is a common cause of leg cramps. Muscles become tight when they are not stretched, when people are inactive, or sometimes when fluid repeatedly accumulates (called edema) in the lower leg.

Low levels of electrolytes (such as potassium, magnesium, or calcium) in the blood can also cause cramps. Low electrolyte levels may result from use of some diuretics, alcoholism, certain endocrine disorders, vitamin D deficiency, or conditions that cause loss of fluids (and thus electrolytes). Electrolyte levels may become low late in pregnancy.

Cramps can occur shortly after dialysis, possibly because dialysis removes too much fluid from the body, removes the fluid to quickly, and/or lowers electrolyte levels.

Other causes include nerve disorders, an underactive thyroid gland (hypothyroidism), and use of certain drugs.

Conditions That Cause or Contribute to Muscle Cramps




Use of certain drugs

Angiotensin II receptor blockers, bronchodilators, cisplatin, clofibrate, diuretics, donepezil, lovastatin, birth control pills (oral contraceptives), pyrazinamide, raloxifene, synthetic parathyroid hormone (teriparatide), tolcapone, or vincristine

Stimulants, such as amphetamines, caffeine, cocaine, ephedrine, nicotine, or pseudoephedrine

Sudden stopping of a drug

Sedatives, such as alcohol, barbiturates, or benzodiazepines

Drugs used to treat insomnia or anxiety


Electrolyte and endocrine disorders

Low levels of potassium, magnesium, or calcium in the blood


Hypothyroidism (an underactive thyroid gland)

Musculoskeletal disorders

Tight calf muscles

Myopathies (disorders that affect muscle)

Structural disorders, such as flat feet or genu recurvatum (a deformity of the knee joint that causes the knee to bend backward)

Nerve disorders

Motor neuron disease (nerve disorders that affect voluntary muscles—those controlled by conscious effort)

Peripheral neuropathies (damage to nerves outside the brain and spinal cord)

Compression of a spinal nerve root

Water balance disorders


Excessive sweating with inadequate replacement of salt or potassium

Effects of dialysis—for example, if too much fluid is removed from the body or if fluid is removed too quickly

Other conditions

Exercise and lifestyle

Cramping during or soon after exercise

Sitting for a long time

Disorders that cause similar symptoms

Some disorders cause symptoms that resemble muscle cramps.

Dystonias are involuntary muscle contractions, but they usually last longer than cramps. Also, they tend to affect other muscles and may affect many other muscles, including any limb muscles as well as those of the back, neck, and voice. In contrast, benign leg cramps and exercise-associated muscle cramping tend to affect the calf muscles.

Tetany is continuous or periodic spasms of muscles throughout the body. These spasms last much longer than muscle cramps and are more widespread. The muscles may also twitch.

Some people feel as if they are having cramps but no muscle contraction occurs (called illusory muscle cramps).

Hardening of the arteries in the legs (peripheral arterial disease) may cause calf pain during physical activity such as walking (see Overview of Peripheral Arterial Disease). This pain is due to inadequate blood flow to muscles, not to muscle contraction as occurs with cramps.


The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.

Warning signs

In people with muscle cramps, the following symptoms and characteristics are of particular concern:

  • Cramps in the arms or trunk

  • Muscle twitching

  • Alcoholism

  • Weakness

  • Cramps that occur after loss of body fluids (dehydration) or use of diuretics

  • Loss of sensation or pain unless they occur at the same time as the cramping

If people have cramps in the arms or trunk or muscle twitching, the cause is more likely to be a disorder (such as an electrolyte or endocrine disorder) or a drug than benign leg cramps or exercise-related muscle cramps.

When to see a doctor

People with muscle cramps should consult a doctor as soon as possible if they also have alcoholism, sudden weakness or loss of sensation, or severe symptoms or if they have lost body fluids (for example, through vomiting, diarrhea, or excessive sweating). Otherwise, people should call their doctor in a day or two to discuss how soon the doctor needs to see them.

What the doctor does

Doctors first ask questions about the person's symptoms and medical history and then does a physical examination. What doctors find during the history and physical examination often suggests a cause and the tests that may need to be done.

Doctors ask the person to describe the cramps, including how long they last, how frequent they are, where they are, whether any event seems to trigger them, and whether any other symptoms are present. They ask about symptoms that suggest clues to the cause:

  • Lack of menstrual periods or menstrual irregularities—symptoms that suggest pregnancy-related leg cramps

  • Vomiting, diarrhea, use of diuretics, excessive exercise, and sweating—symptoms that suggest loss of body fluids or electrolytes

  • Difficulty tolerating cold, weight gain, and coarse, thick skin—symptoms that may indicate hypothyroidism

  • Weakness, pain, or loss of sensation—symptoms that suggest a nerve disorder

The person is also asked about use of drugs and alcohol, recent dialysis treatment, and any association between past dialysis treatments and muscle cramps.

The physical examination focuses first on the nervous system (neurologic examination—see Physical Examination), including assessment of muscles and reflexes. Doctors also inspect the skin for signs of alcoholism, hypothyroidism (such as a puffy face and loss of eyebrow hair), and dehydration.


No tests are routinely done.


Preventing cramps is the best approach. The following measures can help:

  • Not exercising immediately after eating

  • Gently stretching the muscles before exercising or going to bed

  • Drinking plenty of fluids (particularly sports beverages that contain potassium) after exercise

  • Not consuming caffeine (for example, in coffee or chocolate)

  • Not smoking

  • Avoiding drugs that are stimulants, such as ephedrine or pseudoephedrine (a decongestant contained in many products that do not require a prescription but are available only behind the pharmacy counter)

Stretching makes muscles and tendons more flexible and less likely to contract involuntarily. The runner's stretch is the best stretch for preventing calf cramps. A person stands with one leg forward and bent at the knee and the other leg behind with the knee straight—a lunge position. The hands can be placed on the wall for balance. Both heels remain on the floor. The knee of the front leg is bent further until a stretch is felt along the back of the other leg. The greater the distance between the two feet and the more the front knee is bent, the greater the stretch. The stretch is held for 30 seconds and repeated 5 times. Then the set of stretches is repeated on the other side.

Did You Know...

  • Stretching helps prevent cramps because it makes muscles less likely to contract involuntarily—without the person's intending it.

Most of the drugs prescribed to prevent cramps from recurring (including calcium supplements, magnesium carbonate, and benzodiazepines such as diazepam) have not proved to be effective, and they can have side effects. Whether quinine is effective is unclear, but it does have side effects, such as vomiting, vision problems, ringing in the ears, and headaches. Mexiletine (used to treat abnormal heart rhythms) sometimes helps but has many side effects, such as nausea, vomiting, tremors (rhythmic shaking of a body part), and seizures.


If a cramp occurs, stretching the affected muscle often relieves the cramp. For example, for a calf cramp, the person could use a hand to pull the foot and toes upward or could do the runner's stretch.

Key Points

  • Leg cramps are common.

  • The most common causes are benign leg cramps and exercise-associated cramping.

  • Stretching and not consuming caffeine can help prevent muscle cramps.

  • Drug therapy is not usually recommended to prevent muscle cramps.

Resources In This Article

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