Feeling shaky usually comes down to your nervous system being overstimulated, your muscles running low on fuel, or both. The most common everyday causes are low blood sugar, too much caffeine, anxiety, and physical exhaustion. Less often, shakiness points to a medication side effect, a thyroid problem, or a neurological condition that needs attention.
Low Blood Sugar
When blood glucose drops below about 70 mg/dL, your body releases a surge of adrenaline to force stored sugar back into the bloodstream. That adrenaline rush is what produces the shaky, jittery feeling, often along with sweating, a racing heart, and sudden irritability. This is called hypoglycemia, and it’s one of the most common reasons otherwise healthy people feel shaky out of nowhere.
You don’t need to have diabetes for this to happen. Skipping meals, eating mostly simple carbohydrates, exercising hard without eating enough, or drinking alcohol on an empty stomach can all cause a dip that triggers shakiness. The fix is straightforward: eating something with both fast-acting sugar and a source of protein or fat stabilizes your blood glucose within 15 to 20 minutes. If you regularly feel shaky between meals, it’s worth paying attention to how often and how evenly you’re eating throughout the day.
Anxiety and the Stress Response
Anxiety triggers your fight-or-flight system, flooding your body with adrenaline (epinephrine). Adrenaline activates receptors on your skeletal muscles that increase their readiness to move, but when there’s no physical threat to respond to, that extra activation shows up as trembling hands, shaky legs, or a general internal vibration. It can also speed your heart rate, tighten your chest, and make you feel lightheaded, which compounds the sensation of shakiness.
This type of shaking is harmless, though it doesn’t feel that way. It tends to ease once the perceived threat passes and adrenaline levels drop. For people with chronic anxiety or panic disorder, the shakiness can recur frequently enough to become distressing on its own. Breathing techniques that slow your exhale can help dampen the adrenaline response in the moment, but persistent anxiety-related shaking usually responds best to broader anxiety management through therapy, lifestyle changes, or both.
Caffeine and Other Stimulants
Caffeine stimulates your central nervous system and increases adrenaline output, which is exactly why it wakes you up. But past a certain point, that stimulation spills over into tremors, jitteriness, and a racing heart. Research has shown that even a single 150 mg dose of caffeine (roughly the amount in a standard cup of coffee) measurably increases hand tremor compared to a placebo, and the effect is more pronounced in people who don’t regularly consume caffeine.
If you drink multiple cups of coffee, energy drinks, or pre-workout supplements, the cumulative dose can easily push past 400 mg in a day. At that level, shakiness is a predictable side effect for most people. Stimulant medications, including those prescribed for ADHD, can cause the same kind of tremor through a similar mechanism.
Muscle Fatigue After Exercise
If your muscles shake during or after a hard workout, that’s a sign of neuromuscular fatigue rather than a disease. When a muscle is fresh, your brain rotates between different groups of muscle fibers to share the workload smoothly. As those fibers tire out, the firing pattern becomes less coordinated. Research on sustained muscle contractions found that motor units (the bundles of fibers controlled by a single nerve) begin firing in sync as fatigue sets in, and that increased synchronization directly correlates with visible tremor in the muscle.
This is why your legs might shake while holding a wall sit or your arms tremble at the end of a set of pushups. It resolves with rest and adequate nutrition, and it’s not a sign of anything wrong.
Medications That Cause Shakiness
A surprisingly wide range of medications list tremor as a side effect. The most common culprits include asthma inhalers (particularly albuterol), certain antidepressants (SSRIs and tricyclics), lithium, anti-seizure medications, steroids, some heart rhythm drugs, and thyroid hormone replacement when the dose is too high. Even some antibiotics and antiviral medications can cause it.
Drug-induced tremor typically shows up shortly after starting a new medication or increasing a dose. If you notice new shakiness that lines up with a medication change, it’s worth flagging to whoever prescribed it. In many cases, adjusting the dose or switching to a related drug resolves the problem.
Thyroid Problems
An overactive thyroid (hyperthyroidism) revs up your metabolism and amplifies your body’s sensitivity to adrenaline. The result is a fine, fast tremor, typically most noticeable when you hold your hands out in front of you. Studies have measured this tremor at around 7 cycles per second, faster than most other types of shaking. It responds well to medications that block the adrenaline-amplifying effect, which is why beta-blockers are often part of hyperthyroidism treatment.
Other signs of an overactive thyroid include unexplained weight loss, heat intolerance, a rapid or irregular heartbeat, and difficulty sleeping. If shakiness comes packaged with several of these symptoms, a simple blood test can confirm or rule out a thyroid issue.
Low Magnesium and Electrolyte Imbalances
Magnesium plays a key role in how your nerves signal your muscles. When levels drop too low, muscles become hyperexcitable and can tremor on their own. A systematic review of magnesium deficiency found that the most common movement problems were postural tremor (shaking while holding a position, seen in about 23% of cases), intention tremor (shaking that worsens when reaching for something, 10%), and resting tremor (about 8%). The tremors most often affect the upper limbs but can be widespread.
You can become low in magnesium from prolonged sweating, chronic diarrhea, heavy alcohol use, or a diet low in leafy greens, nuts, and whole grains. Low potassium and low calcium can produce similar neuromuscular symptoms. These deficiencies are usually detectable through standard blood work.
Alcohol Withdrawal
For people who drink heavily and regularly, stopping or sharply reducing alcohol intake triggers withdrawal symptoms that include prominent tremors. These can begin within hours of the last drink and typically peak around 72 hours. The shaking happens because alcohol chronically suppresses the brain’s excitatory signals. When alcohol is suddenly removed, the nervous system rebounds into a state of hyperexcitability, producing tremors, agitation, sweating, and sometimes seizures. This type of shakiness can be medically serious and often requires supervised management.
Neurological Conditions
When shakiness is persistent and progressive rather than coming and going with meals or stress, a neurological cause becomes more likely. The two most common are essential tremor and Parkinson’s disease, and they behave differently.
Essential tremor is the more common of the two. It produces shaking primarily during movement or while holding a position, like lifting a cup or writing. It tends to run in families, typically starts gradually, and often affects both hands. The tremor frequency is generally in the 5 to 8 cycles per second range. It can also cause a head tremor that disappears when you lie down.
Parkinson’s tremor is different. It’s most noticeable at rest, when your hand is sitting in your lap, for example, and tends to decrease when you move intentionally. It oscillates more slowly, in the 4 to 6 cycles per second range, and often starts on one side of the body. A distinctive feature is the “re-emergent” tremor: if you hold your arms outstretched, the shaking may not appear immediately but starts after a delay of several seconds. In one study, this delay averaged about 9 seconds in people with Parkinson’s, while it was rare and much shorter in essential tremor.
When Shakiness Needs Urgent Attention
Most shakiness is temporary and explainable. But certain patterns warrant prompt medical evaluation: tremors that start suddenly rather than building gradually, shakiness in anyone under 50 with no family history of tremor, and shaking accompanied by changes in mental clarity, muscle weakness, difficulty walking, or trouble speaking. A rapid heart rate paired with agitation also raises concern, as it can point to thyroid storm, stimulant toxicity, or severe withdrawal. In these situations, getting evaluated quickly matters.