Tremor results from functional hyperexcitability of neuronal loops (mainly through basal ganglia and cerebellum) and structural pathology via neurodegeneration. It can result from lesions in the brainstem, extrapyramidal system, and cerebellum or neurologic injury from ischemia, metabolic disorders, and neurodegenerative diseases.

Medications cause tremors by either exacerbating an underlying physiologic tremor or inducing excitability in muscle receptors and neuronal reflexes.

Physiologic tremor occurs in normal individuals and is evident only when exacerbated by stress, sleep deprivation, medications, or substances. Agents that exacerbate tremor include nicotine, caffeine, alcohol, stimulants, benzodiazepine withdrawal, thyroid supplements, and beta agonist inhalers. Essential tremor, often familial, is clinically impairing and may also exacerbate with stress. This tremor is diagnosed when no other etiologies are identified. A psychogenic tremor is diagnosed when no etiology is identified and tremor has certain characteristics. Disease conditions that cause any type of neurologic injury can result in tremors. Tremor is a common symptom in Parkinson disease and cerebellar degeneration. Wilson disease is a rare systemic disease that often presents with tremor.

Mood stabilizers and antidepressants cause a fine, bilateral, symmetric, dose-related tremor [1]. It usually occurs early in treatment though can develop later. Risk factors are older age and personal or family history of tremors. The tremor sometimes improves with time but usually it is necessary to treat the tremor or stop the offending medication. Among mood stabilizers, prevalence of tremor is lithium > valproate > lamotrigine. Both tricyclic antidepressants and serotonin reuptake inhibitors cause tremors on higher doses, during withdrawal or as a precursor to serious side effects such as serotonin syndrome.

Antipsychotics can cause tremor without other features of parkinsonism. The tremor may be a bilateral action tremor that occurs early in treatment or a tardive tremor that occurs after long-term treatment. Tremor can also be seen along with dystonia and tardive dyskinesia.

The characteristics of tremor associated with different classes of psychotropic medications are described in the table. Also described are features of rest and action tremors.