Causes of Leg Cramps at Night

From the quiet of rest, an intense leg cramp leaves you grabbing at your calf and shouting, “Ouch!” What causes leg cramps at night? Sometimes called a charley horse, learn about these painful muscle contractions and the most common associated conditions and likely causes.

Man sitting on edge of bed at night
PhotoAlto / Frederic Cirou / Getty Images

What Is a Leg Cramp?

A leg cramp is defined as an intensely painful sensation in the leg or foot that is associated with a sudden, involuntary muscle contraction. This contraction makes the affected muscle feel hard or tight. When occurring in the foot, it may cause the toes to curl or extend involuntarily.

Muscle testing during a leg cramp shows spontaneous firing of anterior horn cells, which coordinate muscle activity, followed by discharges within groups of muscle cells at a rate up to 300 times per second (considerably more than with voluntary muscle contractions). The resulting pain may occur from local metabolite disturbances or from local ischemia (reduced blood flow).


This cramping may start abruptly, without any clear precipitating trigger or be preceded by a less painful warning sensation, and may remit spontaneously. Most leg cramps last for several seconds until the intensity fades. At their worst, though more rarely, leg cramps can last for several minutes.

Leg cramps may affect the calf or small muscles within the foot. Less often these cramps may even affect the hamstring muscles at the back of the thigh.

Cramps may occur during wakefulness or during sleep and provoke awakenings. The tenderness may persist for several hours, contributing to insomnia when occurring at night.

Leg cramps out of sleep do not seem to be preceded by any specific identified sleep changes.


Leg cramps are extremely common: nearly every adult 50 years and older has experienced one at least once. In fact, the prevalence increases with age.

Pregnant women also seem to be a higher risk of experiencing leg cramps. Some 40% of pregnant women have leg cramps and delivery often resolves the recurrence of the condition.


Leg cramps may occur less than once per year, but when frequent, may happen with multiple episodes every night. This may quickly lead you to seek the cause.

It is likely that leg cramps occur for many different reasons: the underlying cause remains unknown. Many normal individuals have leg cramps. However, some of the predisposing factors seem to include:

  • Diabetes
  • Amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease)
  • Cramp fasciculation syndrome
  • Peripheral vascular disease
  • Low potassium (hypokalemia)
  • Low calcium (hypocalcemia)
  • Low magnesium (hypomagnesemia)
  • Prior vigorous exercise
  • Prolonged standing at work
  • Dehydration
  • Other fluid/electrolyte disturbances
  • Restricted movement or mobility
  • Endocrine disorders
  • Neuromuscular disorders
  • Liver cirrhosis
  • Hemodialysis

In addition, there are certain medications that may contribute to the risk of developing leg cramps at night. These include oral contraceptives, intravenous iron sucrose, teriparatide, raloxifene, diuretics, long-acting beta agonists, and statins.

If you are concerned about the contribution of prescription medications, speak with your pharmacist or prescribing doctor.

Diagnosis and Treatment

Leg cramps can be very painful and if they occur persistently, consider getting evaluated. It is possible that a careful history and a few blood tests may help to identify potential contributions and help you to sleep better at night without painful interruptions.

It is important to differentiate leg cramps from other similar conditions. Restless leg syndrome may lead to discomfort in the legs with an urge to move when lying down at night to rest. These symptoms are relieved by movement and—importantly—are not associated with muscle contraction or tightening. Periodic limb movements of sleep (PLMS) are repetitive flexing movements, usually at the ankle or knee, that occur during sleep and are not associated with pain. Dystonias are characterized by the simultaneous contraction of conflicting muscle groups, such as the biceps and triceps in the arm, acting spontaneously at the same time.

Treatments, including supplements or even a bar of soap, may provide relief.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Raut TP, Garg RK, Chaudhari TS, Malhotra HS, Singh MK. Focal neuromyotonia as a presenting feature of lumbosacral radiculopathy. Ann Indian Acad Neurol. 2013;16(4):693-5. doi: 10.4103/0972-2327.120464

  2. Behringer M, Moser M, Mccourt M, Montag J, Mester J. A promising approach to effectively reduce cramp susceptibility in human muscles: a randomized, controlled clinical trial. PLoS ONE. 2014;9(4):e94910. doi: 10.1371/journal.pone.0094910

  3. Blyton F, Chuter V, Burns J. Unknotting night-time muscle cramp: a survey of patient experience, help-seeking behaviour and perceived treatment effectiveness. J Foot Ankle Res. 2012;5:7. doi: 10.1186/1757-1146-5-7

  4. UpToDate. Nocturnal Leg Cramps.

Additional Reading

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.