EPMS, short for extrapyramidal symptoms (also called EPS), are movement problems caused by certain medications, most commonly antipsychotics. They show up as muscle stiffness, tremors, slowed movement, or uncontrollable involuntary movements. These side effects occur because the medications block dopamine signaling in the parts of the brain that coordinate smooth, voluntary movement.
EPMS can appear within hours of starting a new medication or develop gradually over months to years. They range from mildly uncomfortable to severely disabling, depending on the type and how quickly they’re caught.
How These Symptoms Happen in the Brain
Your brain relies on dopamine to coordinate muscle movements. Antipsychotic medications work by blocking dopamine receptors, which helps manage conditions like schizophrenia and bipolar disorder. But those same receptors also exist in motor control areas of the brain, and blocking them there disrupts normal movement.
The disruption works in two ways. When dopamine can’t activate one type of receptor (D1), muscles lose their normal ability to relax properly, leading to rigidity. When it can’t activate another type (D2), muscles can’t speed up contractions normally, causing slowness. This is why EPMS often resemble Parkinson’s disease, which also involves dopamine loss in the same brain regions. The connection was first noticed in 1952, when the antipsychotic chlorpromazine was recognized to produce Parkinson-like side effects.
The Four Main Types of EPMS
Acute Dystonia
Dystonia involves sustained muscle contractions that force the body into abnormal postures. It most commonly affects the head and neck, producing symptoms like the neck twisting to one side, jaw clenching, difficulty swallowing, or the eyes rolling upward involuntarily. Sometimes only the hands or a few fingers are affected, and symptoms often worsen during movement like walking. In 95% of cases, acute dystonia appears within 96 hours of starting an antipsychotic or after a significant dose increase. In severe cases, the entire body can arch backward in a distressing full-body spasm.
Parkinsonism
Drug-induced parkinsonism looks very similar to Parkinson’s disease: slowed movements, a resting tremor (often in the hands), muscle rigidity, and a shuffling gait. It typically develops within the first few weeks of treatment. In studies of patients on older antipsychotics like haloperidol, parkinsonism affected about 55% of people. Newer antipsychotics still cause it at notable rates, around 26% with some medications.
Akathisia
Akathisia is an intense inner restlessness that makes it nearly impossible to sit still. People with akathisia feel a constant urge to move, pace, shift weight, or rock back and forth. It’s one of the most distressing forms of EPMS because the discomfort is internal rather than visible to others. Roughly 25% of patients on older antipsychotics develop akathisia.
Tardive Dyskinesia
Unlike the other types, tardive dyskinesia develops slowly after months or years of medication use. It causes repetitive, involuntary movements, most often around the face and mouth: lip smacking, tongue darting, grimacing, or chewing motions. The defining feature of tardive dyskinesia is that it persists even after the medication is stopped. A formal diagnosis requires that the involuntary movements continue for at least one month after discontinuing the drug. Tardive dyskinesia can appear as early as one to six months into treatment, and among patients on older antipsychotics, prevalence averages between 24% and 30%.
Which Medications Cause EPMS
Antipsychotics are by far the most common cause, but any medication that blocks dopamine receptors in the brain can trigger these symptoms. That includes certain anti-nausea medications and some antidepressants (SSRIs have been linked to tardive movements in rare cases).
Older antipsychotics, called first-generation or “typical” antipsychotics, carry the highest risk. In one study of institutionalized patients with schizophrenia, 61.6% of those on first-generation antipsychotics experienced EPMS. About half of patients on high-potency options like haloperidol develop acute symptoms within the first several days of treatment.
Newer, second-generation antipsychotics were designed partly to reduce this risk, and they do cause fewer movement side effects. But the difference isn’t as dramatic as once believed. Some research suggests the risk with newer antipsychotics is more than half that of older ones, not the one-quarter estimate that earlier studies proposed. Among second-generation options, clozapine carries the lowest risk and risperidone the highest. At 12 months of treatment, rates of parkinsonism with second-generation antipsychotics ranged from 37% to 44%, comparable to the 37% seen with some first-generation drugs.
Who Is Most at Risk
Several factors increase the likelihood of developing EPMS. Older age raises risk, as does smoking. Having a history of tremor makes a person about 7 times more likely to develop these symptoms. Prior antipsychotic use nearly quadruples the risk, likely because previous dopamine receptor exposure sensitizes the brain. Interestingly, gender does not appear to significantly affect risk.
Dose also matters. Nearly all antipsychotics can cause EPMS in a dose-dependent manner, meaning higher doses produce more movement problems.
How EPMS Are Detected
The primary screening tool is the Abnormal Involuntary Movement Scale (AIMS), a 12-item assessment where a clinician observes and scores involuntary movements across different body regions. Each movement is rated from zero (none) to four (severe). The American Psychiatric Association recommends AIMS screening every six months for people at high risk of tardive dyskinesia and every 12 months for others. Ideally, a baseline assessment is done before starting antipsychotic treatment so that any new movements can be identified early.
For acute symptoms like dystonia or akathisia, diagnosis is primarily clinical. If abnormal positioning or muscle spasms develop within seven days of starting or increasing a medication, acute dystonia is the likely explanation.
How EPMS Are Managed
The first step for any type of EPMS is usually reducing the dose of the medication causing the problem or switching to a lower-risk antipsychotic. Clozapine, olanzapine, and quetiapine are often considered because they carry less movement-related risk.
For acute dystonia, anticholinergic medications (which counteract the dopamine imbalance affecting motor control) can reverse symptoms relatively quickly. For parkinsonism, the same class of anticholinergics is commonly used, though they come with their own side effects like dry mouth and constipation.
Akathisia is often the hardest to treat. Options include beta-blockers like propranolol, which can reduce the physical restlessness, as well as certain antidepressants. Evidence quality for most akathisia treatments is low, relying more on clinical experience than large trials, so treatment tends to be individualized based on what works for each person.
Tardive dyskinesia is the most challenging form because it can be irreversible. Stopping the offending medication doesn’t always resolve it. Switching to clozapine has shown some benefit in case reports, and specialized medications that reduce dopamine signaling in a different way have been developed specifically for tardive dyskinesia. Early detection through regular AIMS screening remains the most effective strategy, since catching it early improves the chances that symptoms will resolve.