Tremors can be caused by dozens of different things, ranging from too much coffee to serious neurological conditions. The two most common culprits are essential tremor, a largely inherited condition affecting up to 1.6% of people over 75, and Parkinson’s disease, where roughly 88% of patients have tremor as an early symptom. But medications, thyroid problems, low blood sugar, alcohol withdrawal, stress, and fatigue can all trigger tremors too. Understanding the type of tremor you’re experiencing is the first step toward figuring out its cause.
Essential Tremor
Essential tremor is the most common movement disorder, and it gets more frequent with age. Among adults 18 to 40, the diagnosed prevalence is only about 0.06%. By age 65 to 74, it rises to nearly 1%, and past age 75 it reaches 1.6%. Many cases go undiagnosed, so the true numbers are likely higher.
The hallmark of essential tremor is that it shows up during movement or when holding a posture, not at rest. You’ll notice it when you’re reaching for a glass, writing, or holding your arms outstretched. The tremor typically vibrates at 5 to 8 cycles per second, which produces a relatively fine, rapid shaking. It most often affects the hands and arms, though it can involve the head, voice, or legs. About 20 to 30% of people with essential tremor also experience some shaking at rest, but action tremor remains the defining feature. Essential tremor tends to run in families and often worsens gradually over years or decades.
Parkinson’s Disease
Parkinson’s tremor looks and feels different from essential tremor. It’s a slower tremor, cycling at about 4 to 6 times per second, and it classically appears when the hand is resting in your lap or hanging at your side. It often starts on one side of the body. The tremor typically stops or fades when you begin a deliberate movement like picking something up, then may reappear after a delay once you hold a new position. This “re-emergent” quality is distinctive.
About 88% of people with early Parkinson’s disease present with tremor, making it the most recognizable symptom. But Parkinson’s is more than a tremor disorder. It involves the progressive loss of brain cells that produce dopamine, which also leads to stiffness, slowness of movement, and balance problems. If your tremor is accompanied by any of those additional features, that pattern points more toward Parkinson’s than essential tremor.
Medications That Trigger Tremors
A surprising number of common medications can cause or worsen tremors. The shaking is a direct response of the nervous system and muscles to the drug, and it often improves when the medication is adjusted or stopped. Some of the most frequent offenders include:
- Asthma inhalers and bronchodilators (albuterol, theophylline), which stimulate the nervous system as a side effect of opening the airways
- Mood stabilizers like lithium, one of the most well-known tremor-inducing drugs, particularly at higher doses
- Antidepressants, including SSRIs and older tricyclic antidepressants
Drug-induced tremor is usually an action tremor, meaning it appears when you’re using your hands or holding them in a position. If you started a new medication within weeks of noticing a tremor, the timing alone is a strong clue. Don’t stop any medication on your own, but do bring it up with whoever prescribed it.
Thyroid Problems
An overactive thyroid (hyperthyroidism) is one of the most common metabolic causes of tremor. About 76% of people with an overactive thyroid develop a tremor, and the more elevated the thyroid hormone levels, the more intense the shaking tends to be. The tremor is typically fine and fast, most noticeable in the outstretched fingers, and usually affects both sides equally.
Because hyperthyroidism also causes a racing heart, weight loss, heat intolerance, and anxiety, the tremor rarely appears in isolation. If you’re experiencing several of those symptoms together, a simple blood test can check your thyroid function. Treating the underlying thyroid condition usually resolves the tremor.
Low Blood Sugar
When your blood sugar drops too low, your body releases a surge of adrenaline to compensate. That adrenaline rush produces shaking hands, sweating, a pounding heart, and feelings of anxiety. This type of tremor comes on relatively quickly, correlates with missed meals or insulin use in people with diabetes, and resolves once you eat or drink something with sugar. If you notice tremors that reliably appear when you haven’t eaten in a while, blood sugar may be the explanation.
Caffeine and Alcohol
Caffeine is a stimulant that can cause temporary tremors or make an existing tremor noticeably worse. The effect is dose-dependent: a single cup of coffee is unlikely to cause problems for most people, but several cups or energy drinks can push you past the threshold.
Alcohol has a more complex relationship with tremor. In the short term, alcohol actually suppresses tremor, which is why some people with essential tremor notice their shaking improves after a drink. But chronic heavy drinking causes the brain to compensate by ramping up its excitatory signaling and dialing down its calming signals. When alcohol is suddenly reduced or stopped, those compensatory changes are unmasked, producing a state of nervous system hyperexcitability. Tremors from alcohol withdrawal typically begin within hours of the last drink and usually resolve within 5 to 7 days, though mood-related symptoms can linger much longer. Severe alcohol withdrawal tremors can signal a medical emergency.
Stress, Anxiety, and Fatigue
Everyone has a baseline level of involuntary shaking called physiological tremor. It’s normally so small you can’t see it. But certain states amplify it into something visible, a condition called enhanced physiological tremor. Stress, strong emotions, physical exhaustion, and sleep deprivation are the most common amplifiers. The tremor is fine, affects both hands, and appears during action rather than at rest.
This type of tremor is not caused by any neurological disease. It’s your nervous system responding to temporary overload. Once the stress passes or you rest, the tremor fades. If you notice your hands shaking before a presentation or after an intense workout, enhanced physiological tremor is the most likely explanation.
Multiple Sclerosis and Brain Lesions
Damage to the cerebellum, the brain region that coordinates smooth, precise movement, can produce a distinctive type of shaking called intention tremor. This tremor is absent at rest and relatively mild during the middle of a movement, but it dramatically worsens as your hand approaches its target. Reaching to press an elevator button, for example, would produce increasing wobble the closer your finger gets.
Multiple sclerosis (MS) is one of the more common causes of this type of tremor. MS creates patches of damage in the brain and spinal cord, and when those patches hit the cerebellum or the pathways connecting it to other brain regions, tremor results. The tremor in MS is typically large in amplitude, cycling at 2.5 to 7 times per second, and often appears alongside other coordination problems like slurred speech or difficulty with rapid alternating movements. Strokes that affect the same brain areas can produce similar intention tremors.
Functional Tremor
Functional tremor (sometimes called psychogenic tremor) is real shaking that originates from how the brain processes movement rather than from structural damage or degeneration. It’s more common than many people realize. The key diagnostic feature is that the tremor changes when the person is distracted. During an examination, a doctor may ask you to tap a rhythm with your unaffected hand. In functional tremor, the shaking hand will often lock onto the same rhythm as the tapping (called entrainment), or the tremor may pause or shift in frequency during a mentally engaging task. These responses don’t occur with tremors caused by Parkinson’s or essential tremor. Functional tremor is treatable, often through specialized physical therapy and psychological approaches.
How Doctors Tell the Difference
The first step in diagnosing a tremor is observation: when does it appear (rest vs. action), how fast is it, where on the body does it occur, and what makes it better or worse? These details alone can narrow the possibilities substantially.
When the cause remains unclear, imaging can help. A specialized brain scan called a DaTscan measures the health of dopamine-producing brain cells. A normal DaTscan effectively rules out Parkinson’s disease, making it particularly useful for distinguishing Parkinson’s from essential tremor or medication-induced tremor. The scan involves an injection of a tracer substance followed by imaging about 3 to 6 hours later. A trained radiologist reads the image as either normal (symmetrical, comma-shaped patterns in specific brain structures) or abnormal.
Blood tests for thyroid function, blood sugar, and medication levels help identify metabolic and drug-related causes. In some cases, sensors that measure the tremor’s electrical pattern and frequency can detect the variability characteristic of functional tremor. The combination of clinical examination, blood work, and targeted imaging identifies the cause in the vast majority of cases.