Shaking in your right or left thumb is called a tremor or twitch. It’s often a reaction to stress or a muscle twitch. When caused by another condition, it’s usually accompanied by other symptoms.

Here’s what to watch for and when to see your doctor.

Essential tremor is an inherited condition that makes the hands shake. If one of your parents has the gene mutation that causes essential tremor, you have a strong chance of developing this condition later in life.

You can get essential tremor at any age, but it’s most common in older adults.

The tremor usually appears during movements like writing or eating. The shaking may get worse when you’re tired, stressed, or hungry, or after you ingest caffeine.

Repeating the same motion over and over again — like playing a video game or typing on a keyboard — can damage the muscles, nerves, tendons, and ligaments in your hands.

Repetitive motion injuries are common in people who work on assembly lines or use vibrating equipment.

Other symptoms of a repetitive motion injury include:

  • pain
  • numbness or tingling
  • swelling
  • weakness
  • difficulty moving

If you keep repeating the movement, you may eventually lose function in the affected finger or thumb.

Shaking may be a sign that you’re under a lot of stress. Strong emotions can make your body tense up or feel restless.

Stress can worsen shaking conditions like essential tremor. And it can trigger repeated muscle spasms called tics, which look like twitching movements.

It can also cause:

  • irritability or sadness
  • fatigue
  • stomachache
  • headache
  • trouble sleeping
  • difficulty focusing

Your body goes into fight-or-flight mode when you’re anxious. Your brain triggers the release of stress hormones like adrenaline. These hormones increase your heart rate and breathing, and make your brain more alert to handle the impending threat.

Stress hormones can also make you shaky and jittery. You may notice that your thumb or other parts of your body twitch.

Anxiety can also cause symptoms like:

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

A lack of sleep does more than cause fatigue and crankiness. Too little shut-eye could also make you shaky.

Sleep has direct effects on your nervous system. How much you sleep can affect the release of chemicals that are involved in movement.

Research finds that extreme sleep deprivation makes the hands shake. The shaking can be so intense that it’s hard to perform tasks requiring precise movements.

It can also result in:

  • memory problems
  • trouble concentrating
  • moodiness or irritability
  • slowed reflexes
  • headache
  • dizziness
  • loss of coordination
  • overall weakness
  • poor decision-making abilities

A cup of coffee in the morning may wake you up and make you feel more alert. But drinking too much coffee could leave you shaky.

The shaking is due to the stimulant effect of caffeine. Each cup of coffee contains about 100 milligrams (mg) of caffeine. The recommended amount of caffeine is 400 mg daily, which is about three or four cups of coffee. Drinking more than four cups of coffee or other caffeinated beverages a day could make you jittery.

Shaking can also be a side effect of stimulant drugs called amphetamines. These drugs are used to treat conditions like attention deficit hyperactivity disorder and help with weight loss.

Other stimulants — like cocaine and methamphetamine — are sold illegally and used to get high.

Symptoms of excessive caffeine or stimulant intake include:

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

Shaking in your hands or other parts of your body can be a side effect of drugs you take. Certain medications cause shaking via their effects on your nervous system and muscles.

Drugs that are known to cause shaking as a side effect include:

  • antipsychotic drugs called neuroleptics
  • asthma bronchodilator medications
  • antidepressants, such as selective serotonin reuptake inhibitors (SSRIs)
  • bipolar disorder drugs, like lithium
  • reflux drugs, like metoclopramide (Reglan)
  • corticosteroids
  • weight loss drugs
  • thyroid medication (if you take too much)
  • seizure medications such as sodium valproate (Depakote) and valproic acid (Depakene)

The shaking should stop once you stop taking the drug. You shouldn’t stop taking prescribed medications without your doctor’s approval, though.

If you think your medication is to blame, talk to your doctor. They can help you safely come off of the medication and, if needed, prescribe an alternative.

In the middle of each wrist is a narrow tunnel that’s surrounded by connective tissue and bones. This is called the carpal tunnel. The median nerve runs through this passageway. It provides feeling to your hand and also controls some of the muscles in the hand.

Repeating the same hand and wrist motions again and again can make the tissues around the carpal tunnel swell up. This swelling puts pressure on the median nerve.

Symptoms of carpal tunnel syndrome include weakness, numbness, and tingling in your fingers or hand.

Parkinson’s is a brain disease caused by damage to nerve cells that produce the chemical dopamine. Dopamine helps keep your movements smooth and coordinated.

A lack of dopamine causes classic Parkinson’s symptoms like shaking in the hands, arms, legs, or head while your body is at rest. This shaking is called a tremor.

Other symptoms include:

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

ALS, also called Lou Gehrig’s disease, damages the nerve cells that control movement (motor neurons). Motor neurons normally send messages from your brain to your muscles to facilitate movement. In ALS, these messages can’t get through.

Over time the muscles weaken and waste away (atrophy) from lack of use. As the muscles get weaker it becomes harder to use them. The strain of trying to simply lift your arm can make your muscles twitch and shake, which looks like a tremor.

Other ALS symptoms include:

  • weak muscles
  • stiff muscles
  • cramps
  • slurred speech
  • trouble chewing and swallowing
  • trouble with small movements like writing or buttoning a shirt
  • difficulty breathing

Some tremors are temporary and don’t require treatment.

If the tremor persists, it may be tied to an underlying cause. In this case, treatment depends on what condition is causing the shaking.

Your doctor may recommend:

  • Stress management techniques. Meditation, deep breathing, and progressive muscle relaxation can help control shaking that’s caused by stress and anxiety.
  • Avoiding triggers. If caffeine sets off your shaking, limit or skip foods and drinks that contain it, such as coffee, tea, soda, and chocolate.
  • Massage. A massage can help relieve stress. Research also finds it may help treat shaking due to essential tremor.
  • Stretching. Stretching can help relieve tight muscles and prevent them from spasming.
  • Medication. Treating the condition that causes the shaking, or taking a medication like an anti-seizure drug, beta-blocker, or tranquilizer, can sometimes calm tremors.
  • Surgery. A type of surgery called deep brain stimulation can treat shaking caused by essential tremor.

Occasional shaking probably isn’t any reason for concern. You should see your doctor if the tremor:

  • doesn’t go away after a couple of weeks
  • is constant
  • interferes with your ability to write or do other activities of daily living

You should also see your doctor if any of these symptoms occur along with the shaking:

  • pain or weakness in your hand or wrist
  • tripping or dropping things
  • slurred speech
  • trouble standing or walking
  • loss of balance
  • trouble breathing
  • dizziness
  • fainting