“The shakes” is a general term for involuntary trembling or shaking in the body, most often in the hands. It’s not a single condition but a symptom with dozens of possible causes, ranging from too much coffee to a neurological disorder. Most episodes are temporary and harmless, triggered by something like low blood sugar, caffeine, anxiety, or cold temperatures. Persistent or worsening shaking, however, can signal something that needs medical attention.
How Shaking Works in the Body
Shaking happens when muscles contract and relax rapidly in a rhythmic pattern. Sometimes the brain sends these signals intentionally, like when you shiver to generate heat. Other times, the signals are misfires from the nervous system, the result of chemical imbalances, or a side effect of something you consumed.
Doctors classify shaking based on when it happens. Rest tremor occurs when your muscles are relaxed, like when your hand shakes in your lap. Action tremor happens during movement, such as when you reach for a glass of water or try to write. This distinction matters because different causes tend to produce different patterns.
Caffeine, Hunger, and Other Everyday Triggers
The most common reason healthy people get the shakes is something they ate, drank, or skipped. Caffeine is a major culprit. Up to 400 milligrams a day (roughly four cups of coffee) is generally safe for most adults, but going beyond that can cause muscle tremors, restlessness, and a racing heart. Some people are more sensitive and notice shakiness at much lower doses.
Low blood sugar is another frequent trigger. When blood glucose drops below about 70 mg/dL, the body releases stress hormones that cause sweating, anxiety, a racing heartbeat, and visible trembling. This is common in people with diabetes who take insulin, but it can happen to anyone who hasn’t eaten in a long time or has just finished intense exercise. Eating something with carbohydrates usually resolves it within minutes.
Stress and anxiety activate the same fight-or-flight response, flooding the body with adrenaline. That surge can make your hands shake, your legs feel weak, and your voice quiver. Sleep deprivation amplifies the effect. If you’ve ever noticed shaky hands after a terrible night of sleep and too much coffee, you’ve experienced multiple triggers stacking on top of each other.
Shaking With a Fever
Intense, full-body shaking during an illness is called a rigor. It looks and feels different from a hand tremor. Your muscles contract forcefully and uncontrollably, often making your teeth chatter and your whole body visibly shake.
This happens because an infection resets your brain’s internal thermostat to a higher temperature. Immune molecules travel through the bloodstream to the hypothalamus, the part of the brain that regulates body heat, and effectively tell it that 98.6°F is no longer warm enough. Your body responds the same way it would if you walked outside in freezing weather: it generates heat through rapid muscle contractions. Once your temperature reaches the new set point, the shaking stops and you feel flushed and hot instead.
Alcohol and Drug Withdrawal
Shaking is one of the hallmark signs of alcohol withdrawal. When someone who has been drinking heavily for an extended period stops or significantly cuts back, tremors typically begin within 6 to 24 hours after the last drink. Symptoms tend to peak between 24 and 72 hours, then gradually improve for most people with mild to moderate withdrawal.
The shaking is usually most noticeable in the hands but can affect other parts of the body. It often comes alongside anxiety, insomnia, sweating, and headache. In severe cases, withdrawal can progress to confusion, hallucinations, or seizures, which is why stopping heavy alcohol use cold turkey without medical support can be dangerous.
Withdrawal from benzodiazepines, opioids, and certain other substances can produce similar tremors through related mechanisms. The nervous system, accustomed to the sedating effects of the substance, becomes overexcitable once it’s removed.
Medications That Cause Tremors
A number of common prescription medications list tremors as a side effect. The shaking is typically symmetrical (affecting both hands equally) and appears during movement rather than at rest. It often starts shortly after beginning a new medication or increasing the dose.
Drug classes most commonly associated with tremors include antidepressants (both SSRIs and older tricyclic types), lithium (used for bipolar disorder), certain anti-seizure medications like valproate, bronchodilators used for asthma, and some immunosuppressive drugs used after organ transplants. Valproate is somewhat unusual in that tremor can appear even at a stable dose after weeks or months of use, rather than right away.
If a medication is causing noticeable shaking, the typical approach is adjusting the dose or switching to an alternative. It’s not something you should change on your own, but it’s worth bringing up at your next appointment.
Essential Tremor
Essential tremor is the most common movement disorder and the most likely neurological explanation for persistent shaking. It primarily affects the hands during action, meaning you notice it when you’re pouring a drink, eating soup, or writing, not when your hands are resting in your lap. It can also cause head bobbing or a quivering voice.
The tremor frequency in essential tremor is typically 5 to 8 cycles per second, which looks like a fine, rapid shaking. It tends to run in families, often starts gradually in one hand and eventually affects both, and generally worsens slowly over years or decades. Stress, fatigue, and caffeine make it more noticeable. Many people with mild essential tremor never need treatment, though options exist for those whose daily life is affected.
How Parkinson’s Tremor Differs
Parkinson’s disease also causes shaking, but the pattern is distinct. The classic Parkinson’s tremor happens at rest, when the hand is relaxed in the lap or hanging at the side. It often looks like a “pill-rolling” motion between the thumb and fingers. The shaking tends to stop or decrease when you reach for something, which is the opposite of essential tremor.
About 90% of people with Parkinson’s develop a rest tremor at some point. The tremor frequency is slower than essential tremor, typically 4 to 6 cycles per second. It may start on one side of the body and can affect the legs, jaw, or chin in addition to the hands. Parkinson’s tremor also comes with other symptoms like stiffness, slowness of movement, and balance problems, which help distinguish it from essential tremor.
One useful clue: if you hold your arms outstretched and a tremor appears after a delay of several seconds, that “re-emergent” pattern is more characteristic of Parkinson’s. In essential tremor, the shaking starts almost immediately when you extend your arms.
When Shaking Needs Attention
Occasional, brief episodes of shaking after too much coffee, a skipped meal, or a stressful moment are normal and nothing to worry about. The shakes that warrant a closer look are the ones that persist, worsen, or appear suddenly without an obvious explanation.
Sudden onset of tremor is a red flag. It can point to a stroke, a brain lesion, toxic exposure, or a demyelinating condition. Shaking accompanied by confusion, slurred speech, or loss of coordination also needs prompt evaluation. A tremor that starts on one side of the body, progressively worsens, or interferes with daily tasks like buttoning a shirt or holding a cup is worth discussing with a doctor, even if it’s been present for a while.
For most people searching “what is the shakes,” the answer turns out to be something benign and temporary. But because the symptom overlaps with so many conditions, a tremor that doesn’t resolve or doesn’t have a clear trigger is always worth investigating.