Use of certain medications and other substances

Stimulants, such as amphetamines, caffeinenicotine

Sudden stopping of a drug or medication

Sedatives, such as alcohol, barbiturates, or benzodiazepines

Medications used to treat insomnia or anxiety

Disorders

Metabolic and hormonal (endocrine) disorders

Low levels of potassium (hypokalemia), low levels of magnesium (hypomagnesemia), or low levels of calcium (hypocalcemia)

Alcohol use disorder

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

Dehydration

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