Hand tremors are caused by misfiring signals in the brain’s motor circuits, and the two most common culprits are essential tremor and Parkinson’s disease. But dozens of other conditions can make your hands shake, from an overactive thyroid to medication side effects to simply drinking too much coffee. The key to figuring out what’s behind a tremor is noticing when it happens: at rest, during movement, or while holding a position.
Essential Tremor: The Most Common Cause
Essential tremor is by far the leading cause of hand tremors. A large meta-analysis covering more than 540,000 people across 23 countries found a prevalence of about 1.3% across all ages, rising to nearly 6% in people 65 and older. In people over 90, small studies have found rates above 20%. If you developed tremors before age 40, there’s a good chance other family members have the same condition.
The defining feature of essential tremor is that shaking starts when you try to use your hands. You might notice it while eating, writing, buttoning a shirt, or pouring a drink. Then, as soon as you stop moving, the tremor goes away. This is the opposite pattern from Parkinson’s, and it’s the single most useful clue for telling the two apart. Essential tremor oscillates at 4 to 12 cycles per second, which typically feels like a fine, rapid shaking.
The underlying problem traces back to the cerebellum, the brain region that coordinates smooth movement. Abnormal rhythmic activity in the circuits connecting the cerebellum to the motor cortex (via a relay station in the thalamus) produces the involuntary oscillation. In animal studies, directly stimulating this cerebellar-to-thalamus pathway produces tremor at the exact frequency of the stimulation, confirming this circuit as the source.
Parkinson’s Disease Tremor
Parkinson’s causes a very different type of shaking. The tremor appears when your hands are resting in your lap or hanging at your side, producing a slow, rhythmic, back-and-forth motion sometimes described as “pill-rolling.” It oscillates at 3 to 6 cycles per second, noticeably slower than essential tremor. Stress and anxiety make it worse, but intentionally reaching for something actually quiets it down.
Parkinson’s tremor results from the loss of cells that produce dopamine, a chemical messenger essential for smooth, controlled movement. The resting tremor is often one of the earliest visible signs, and it usually starts on one side of the body before eventually affecting both. When the diagnosis is uncertain, a specialized brain imaging scan can measure dopamine activity. In patients with established symptoms, this scan correctly identifies Parkinson’s about 97% of the time, with a 98% accuracy rate for ruling it out.
Medications and Substances
A long list of medications can trigger hand tremors as a side effect. Some of the most common include:
- Mood stabilizers like lithium
- Antidepressants, including SSRIs and tricyclics
- Asthma inhalers containing albuterol or theophylline
- Seizure medications like valproate
- Stimulants, including caffeine and amphetamines
- Heart rhythm medications like amiodarone
- Immune-suppressing drugs used after organ transplants
- Too much thyroid replacement medication
- Steroids and certain antibiotics
Alcohol and nicotine can also cause tremors. If your hand shaking started or worsened around the time you began a new medication, that’s worth flagging. Drug-induced tremors often improve once the dose is adjusted or the medication is switched.
Thyroid Problems and Blood Sugar Drops
An overactive thyroid gland (hyperthyroidism) speeds up your entire metabolism, and one of its hallmark symptoms is a fine trembling in the hands and fingers. The excess thyroid hormone essentially puts your nervous system into overdrive. You’ll typically notice other signs alongside the tremor: unexplained weight loss, a rapid or irregular heartbeat, feeling hot when others are comfortable, and anxiety or irritability.
Low blood sugar triggers tremors through a different mechanism. When glucose drops too low, your body releases adrenaline to mobilize energy stores, and that surge of adrenaline makes your hands shake. This is common in people with diabetes who take insulin, but it can also happen in anyone who hasn’t eaten for a long time. The tremor resolves quickly once you eat something.
Physiological Tremor: The Normal Kind
Everyone has a tiny tremor in their hands at all times. It’s called physiological tremor, and it oscillates at 8 to 13 cycles per second, fast enough that you usually can’t see it. Certain situations amplify this normal tremor to the point where it becomes visible: anxiety, fatigue, too much caffeine, skipped meals, or withdrawal from alcohol. This type of tremor is fine and rapid, affecting both hands equally, and it disappears once the trigger is removed.
If your hands only shake during stressful moments, after your third cup of coffee, or when you’re sleep-deprived, you’re likely dealing with an exaggerated physiological tremor rather than a neurological condition.
Cerebellar and Intention Tremors
Damage to the cerebellum from conditions like multiple sclerosis, stroke, or chronic heavy alcohol use produces what’s called an intention tremor. This type gets worse the closer your hand gets to a target. If you’re reaching for a glass of water, the shaking intensifies right as your fingers approach the glass. Intention tremors are slow, oscillating at less than 4 cycles per second, and they look coarser and more irregular than essential tremor.
In multiple sclerosis, the tremor often has a pseudorhythmic quality, meaning it looks rhythmic but doesn’t follow a consistent beat the way essential tremor or Parkinson’s tremor does. Some people with MS develop a fine postural tremor that’s barely visible and goes largely unnoticed, while others experience more disabling shaking during everyday tasks.
How Tremors Are Evaluated
Neurologists rely heavily on observation to categorize tremors. They’ll ask you to hold your arms out in front of you (testing for postural tremor), rest your hands in your lap (testing for resting tremor), and reach for objects or touch your nose (testing for intention tremor). One particularly useful tool is the Archimedes spiral: you’re asked to draw a spiral on paper, and the drawing captures the frequency, size, and direction of the tremor in a way that reveals diagnostic patterns.
Handwriting samples also help. The finished script can show the frequency and amplitude of oscillatory movements, and sometimes a tremor appears during one type of pen movement but not another. These simple pen-and-paper tasks can be compared over time to track whether a tremor is progressing or responding to treatment. When the cause still isn’t clear from the physical exam, imaging or blood tests can check for thyroid problems, dopamine loss, or structural brain changes.
What Affects How Severe a Tremor Gets
Regardless of the underlying cause, several factors reliably make hand tremors worse. Emotional stress and anxiety amplify nearly every type of tremor. Caffeine and other stimulants increase the excitability of motor circuits. Fatigue, sleep deprivation, and low blood sugar all lower the threshold for visible shaking. Cold temperatures can also worsen tremors by increasing muscle tension.
For many people, hand tremors remain mild and more of an annoyance than a disability. Essential tremor, however, is progressive in some cases, gradually increasing in amplitude over years or decades. Parkinson’s tremor tends to change character over time as the disease advances, sometimes becoming less prominent while other movement symptoms like stiffness and slowness take over. Tracking how your tremor behaves, when it appears, and what makes it better or worse gives your doctor the clearest picture of what’s causing it.