An uncontrollable shaking in your legs is called a tremor. Shaking isn’t always a cause for worry. Sometimes it’s simply a temporary response to something that’s stressing you out, or there’s no obvious cause.

When a condition is causing shaking, you’ll usually have other symptoms. Here’s what to watch for and when to see your doctor.

Tremors can feel like RLS. The two conditions aren’t the same, but it’s possible to have tremors and RLS together.

A tremor is simply a shaking in your leg or other body part. Moving the affected limb doesn’t relieve the shaking.

By contrast, RLS makes you feel an uncontrollable urge to move your legs. Often this feeling strikes at night, and it can rob you of sleep.

In addition to shaking, RLS causes a crawling, throbbing, or itching sensation in your legs. You can relieve the twitchy feeling by moving.

A type of shaking called essential tremor may be passed down through families. If your mother or father has a gene mutation that causes essential tremor, you have a high chance of getting this condition later in life.

Essential tremor usually affects the hands and arms. Less often, the legs can shake, too.

Scientists haven’t yet discovered which genes cause essential tremor. They believe a combination of a few genetic mutations and environmental exposures may increase your risk of developing this condition.

Some people subconsciously bounce their foot or leg while focusing on a task — and it may actually serve a useful purpose.

Research in children with attention deficit hyperactivity disorder (ADHD) suggests that repetitive movements improve concentration and attention.

The shaking could help distract the part of your brain that’s bored. With that part of your brain occupied, the rest of your brain can focus on the task at hand.

Shaking legs can also signal that you’re bored. The shaking releases tension that’s stored up when you’re forced to sit through a long lecture or a dull meeting.

Constant bouncing in your leg might also be a motor tic. Tics are uncontrollable, quick movements that give you a feeling of relief.

Some tics are temporary. Others can be signs of a chronic disorder like Tourette syndrome, which also includes vocal tics.

When you’re anxious, your body goes into fight-or-flight mode. Your heart pumps out extra blood to your muscles, readying them to run or engage. Your breath comes faster and your mind becomes more alert.

Hormones like adrenaline fuel the fight-or-flight response. These hormones can also make you shaky and jittery.

Along with shaking, anxiety can trigger symptoms like:

  • a pounding heart
  • nausea
  • unsteady breathing
  • sweating or chills
  • dizziness
  • a feeling of impending danger
  • overall weakness

Caffeine is a stimulant. A cup of coffee can wake you up in the morning and makes you feel more alert. But drinking too much may make you jittery.

The recommended amount of caffeine is 400 milligrams per day. This is equivalent to three or four cups of coffee.

Stimulant drugs called amphetamines also cause shaking as a side effect. Some stimulants treat ADHD and narcolepsy. Others are sold illegally and used recreationally.

Other symptoms of caffeine or stimulant overload include:

  • a fast heartbeat
  • insomnia
  • restlessness
  • dizziness
  • sweating

Drinking alcohol alters levels of dopamine and other chemicals in your brain.

Over time, your brain becomes accustomed to these changes and more tolerant to alcohol’s effects. That’s why people who drink heavily must drink increasingly larger amounts of alcohol to produce the same effects.

When someone who drinks heavily suddenly stops using alcohol, they may develop withdrawal symptoms. Tremors are one symptom of withdrawal.

Others symptoms of alcohol withdrawal include:

  • nausea
  • vomiting
  • anxiety
  • headache
  • a fast heartbeat
  • irritability
  • confusion
  • insomnia
  • nightmares
  • hallucinations
  • seizures

If you or someone you know is experiencing severe alcohol withdrawal symptoms, seek medical attention.

Tremor is a side effect of drugs that affect your nervous system and muscles.

Drugs that are known to cause shaking include:

Stopping the drug should also stop the shaking. However, you should never discontinue prescribed medications without your doctor’s approval.

Your doctor can explain how to wean yourself off of the medication, if needed, and prescribe an alternative medication.

An overactive thyroid gland (hyperthyroidism) can cause shaking. The thyroid gland produces hormones that regulate your body’s metabolism. Too much of these hormones send your body into overdrive.

Other symptoms include:

  • a fast heartbeat
  • increased appetite
  • anxiety
  • weight loss
  • sensitivity to heat
  • changes in menstrual periods
  • insomnia

ADHD is a brain disorder that makes it hard to sit still and pay attention. People with this condition have one or more of these three symptom types:

  • trouble paying attention (inattention)
  • acting without thinking (impulsivity)
  • overactivity (hyperactivity)

Shaking is a symptom of hyperactivity. People who are hyperactive may also:

  • have trouble sitting still or waiting their turn
  • run around a lot
  • talk constantly

Parkinson’s is a brain disease that affects movement. It’s caused by damage to nerve cells that produce the chemical dopamine. Dopamine normally keeps movements smooth and coordinated.

Shaking in the hands, arms, legs, or head is one common symptom of Parkinson’s disease.

Other symptoms include:

  • slowed walking and other movements
  • stiffness of the arms and legs
  • impaired balance
  • poor coordination
  • difficulty chewing and swallowing
  • trouble speaking

MS is a disease that damages the protective covering of nerves in the brain and spinal cord. Damage to these nerves interrupts the transmission of messages to and from the brain and body.

Which MS symptoms you have depends on which nerves are damaged. Damage to nerves that control muscle movement (motor nerves) can cause tremors.

Other symptoms may include:

  • numbness or weakness on one side of the body
  • double vision
  • vision loss
  • tingling or electric shock sensations
  • fatigue
  • dizziness
  • slurred speech
  • bladder or bowel problems

Damage to the nerves that control muscle movement can make you shake. A number of conditions cause nerve damage, including:

Other symptoms of nerve damage include:

  • pain
  • numbness
  • a pins-and-needles or tingling sensation
  • burning

Doctors classify tremors by their cause and how they affect people.

  • Essential tremors. This is one of the most common types of movement disorders. The trembling typically affects the arms and hands, but any part of the body can shake.
  • Dystonic tremors. This tremor affects people with dystonia, a condition in which faulty messages from the brain cause the muscles to overreact. Symptoms range from shaking to unusual postures.
  • Cerebellar tremors. These tremors involve slow movements on one side of the body. The shaking starts after you initiate a movement, like going to shake hands with someone. Cerebellar tremors are caused by a stroke, tumor, or other condition that damages the cerebellum.
  • Psychogenic tremors. This type of tremor starts suddenly, often during stressful periods. It usually involves the arms and legs, but it can affect any body part.
  • Physiologic tremors. Everyone shakes a little bit when they move or stay in one pose for a while. These movements are perfectly normal and are usually too small to notice.
  • Parkinsonian tremors. Tremor is a symptom of Parkinson’s disease. The shaking starts while you’re at rest. It may only affect one side of your body.
  • Orthostatic tremors. People with orthostatic tremors experience a very fast shaking in their legs when they stand up. Sitting down relieves the tremor.

Some tremors are temporary and unrelated to an underlying condition. These tremors typically don’t require treatment.

If the tremor persists, or you’re experiencing other symptoms, it may be tied to an underlying condition. In this case, treatment depends on what condition is causing the shaking.

Your doctor may recommend:

  • Practicing stress management techniques. Deep breathing, progressive muscle relaxation, and meditation can help control shaking from stress and anxiety.
  • Avoiding triggers. If caffeine sets off your shaking, avoiding coffee, tea, sodas, chocolate, and other foods and drinks that contain it can stop this symptom.
  • Massage. A massage can help relieve stress. Research also suggests it may help treat shaking due to essential tremor and Parkinson’s disease.
  • Stretching. Yoga — an exercise program that combines deep breathing with stretches and poses — can help control tremors in people with Parkinson’s disease.
  • Medication. Treating the underlying condition, or taking a medication like an antiseizure drug, beta-blocker, or tranquilizer, can help calm tremors.
  • Surgery. If other treatments aren’t working, your doctor may recommend deep brain stimulation or another surgery to relieve tremors.

Occasional leg shaking probably isn’t any cause for concern. But if the tremor is constant and it interferes with your daily life, see your doctor.

Also see your doctor if any of these symptoms occur alongside shaking:

  • confusion
  • difficulty standing or walking
  • trouble controlling your bladder or bowels
  • dizziness
  • vision loss
  • sudden and unexplained weight loss