Leg cramps at night: causes, red flags and when to get it checked

A cramp is an involuntary, sustained contraction of a muscle. At night the foot is often pointed, which shortens the calf, and nerves that control the muscle may fire spontaneously. The mechanism is not fully understood, but fatigue, nerve excitability and reduced fluid or salt balance have all been implicated.

• No clear cause (idiopathic), particularly in older adults.

• Pregnancy, especially the second and third trimesters.

• Dehydration, strenuous exercise earlier in the day, standing for long periods and sleeping with toes pointed.

• Medicines: diuretics, statins, calcium channel blockers, salbutamol, some chemotherapy and contraceptive pills.

• Alcohol use and low magnesium, potassium or calcium.

• Peripheral arterial disease, venous disease and nerve compression in the spine (lumbar stenosis).

• Underactive thyroid, kidney disease, liver disease and diabetes.

• Motor neurone disease and other neuromuscular conditions, which are rare and have progressive weakness.

Cramps with persistent weakness, muscle wasting, swelling or redness of a calf, skin changes or leg ulcers, calf pain on walking that eases with rest (claudication), numbness, cramps affecting many muscles and unexplained weight loss need assessment.

• Call 999 or go to A&E: a swollen, painful calf with breathlessness or chest pain, or a cold, pale painful leg.

• Same-day GP: one swollen, red or painful calf that does not settle after a cramp (possible clot).

• GP within weeks: frequent cramps, cramps with weakness or muscle wasting.

• Routine: occasional night cramps that settle quickly.

The doctor asks how often, how long, which muscles, medicines, alcohol, fluid intake, exercise, pregnancy and other illnesses. They examine the legs for swelling, pulses, skin changes, muscle bulk and strength, and reflexes.

• Usually none for occasional cramps with a normal examination.

• Blood tests: electrolytes (potassium, calcium, magnesium), kidney, liver, thyroid, glucose, creatine kinase.

• Ankle-brachial index or arterial Doppler: if circulation is poor.

• Nerve conduction studies and EMG: if neuromuscular disease is suspected.

• Review of medicines that might trigger cramps.

During a cramp, straighten the leg and pull the toes toward the shin, stand and walk, or massage the muscle. Stretch the calves gently before bed, stay hydrated, and avoid heavy alcohol in the evening. Keep bedding loose so toes are not pointed. Quinine is no longer routinely recommended because of side effects, and magnesium supplements have limited evidence.

The NHS route is a GP for review of medicines and blood tests. Private physiotherapy and GP review are available, with specialist assessment if neuromuscular disease is suspected.