Definition

Drug-induced tremor is a tremor caused by the consumption of drugs. A tremor is a rhythmic and uncontrollable movement of a body part. Tremors appear as shaking and typically occur when the patient is moving a limb, although they can also appear while the patient is at rest.

The movements caused by tremors are usually rapid. Generally, the tremors that occur are not associated with other symptoms. Drug-induced tremor is a common movement-related medical condition that can be caused by antipsychotic, anticonvulsant, and antidepressant medications. Certain drugs can cause tremors or worsen existing tremors, especially in patients with Parkinson's disease or similar conditions.

Causes

Drug-induced tremors can be caused by the nervous and muscular systems' response to certain medications or as a result of withdrawal from drugs or alcohol. It can also worsen pre-existing tremor conditions.

Medications that can cause tremors include:

• Anticonvulsants used in the treatment of epilepsy and bipolar disorder, such as valproic acid or divalproex sodium.
• Bronchodilators used to widen the airways in asthma patients, such as theophylline and salbutamol.
• Immunosuppressants given to organ transplant recipients.
• Certain antidepressants and mood stabilizers.
• Stimulants like caffeine and amphetamines.
• Some antivirals (e.g., acyclovir) and antibiotics.
• Alcohol and nicotine.
• Certain blood pressure medications and heart drugs.
• Excessive thyroid medications (levothyroxine).
• Tetrabenazine, used to treat hyperkinetic movement disorders.
• Epinephrine and norepinephrine.

Risk factor

Risk factors for drug-induced tremor include people who consume the aforementioned medications. However, some individuals are more at risk than others, such as:

• Elderly individuals.
• Males.
• Those required to take multiple medications (at least five).
• Patients on high doses of medications.

Symptoms

Symptoms of tremor can affect the hands, arms, head, or eyelids. The lower body is rarely affected. Symptoms may include nodding of the head or a trembling voice while speaking.

Tremors usually occur rapidly and may affect one side of the body or both sides with varying intensity. Tremors can occur:

• Episodically, typically an hour after taking a medication.
• Intermittently, disappearing and reappearing with activity but not always.
• Sporadically, occurring at random times.

Types of tremors can vary, appearing during limb movement, while at rest, or when muscles are relaxed. Drug-induced tremors often resemble essential tremors or Parkinsonian tremors, depending on the medication.

Diagnosis

Medical interview and physical examination

Diagnosis usually begins with a doctor asking about your symptoms and medical history. Keeping a record of all medications taken helps in making a diagnosis. You should also inform the doctor about the frequency of the tremors. The tremor's speed can help identify the causative drug.

Some characteristics that distinguish drug-induced tremors from Parkinson's disease include:

• Symptoms occur on both sides of the body, while Parkinson's usually affects one side.
• Symptoms stop after discontinuing the drug. Parkinson's is a chronic and progressive disease.
• No brain function decline in drug-induced tremor, unlike Parkinson's which involves specific brain area deterioration.

Laboratory tests

Doctors may rule out other diagnoses with blood tests. These can detect chemical imbalances in your blood. Thyroid issues can also cause tremors, so hormone levels may be checked.

Imaging

Imaging tests like computed tomographic scans (CT scans) or magnetic resonance imaging (MRI) may be performed. These give doctors a view of your brain, helping to rule out brain damage that could cause tremors.

Management

To treat drug-induced tremors, a doctor may ask you to stop the medication causing the tremor. However, you need to discuss the consequences of stopping the medication for your condition with your doctor. Alternative therapies that do not cause or less frequently cause tremors may be suggested. Symptoms usually disappear within 4-18 months after stopping the drug.

Doctors will evaluate whether you need additional treatment, considering factors such as:

• The functional impact of the tremor.
• Side effects accompanying the tremor.
• Whether the patient is willing to take additional medication or stop the suspected tremor-causing drug.

If the tremor might be caused by other external factors and there is no clear evidence linking it to a drug, possible toxin exposure should be considered.

Generally, drug-induced tremors improve after discontinuing the causative medication. Consult your doctor before stopping any medication. Discuss alternative drugs or dosage reductions.

Complications

Severe tremors can interfere with daily activities, such as fine motor tasks like writing or eating and drinking. Additionally, individuals with tremors may experience stress due to embarrassment, especially in public.

Drug-induced tremors usually subside after stopping the causative drug. However, persistent tremors (tardive tremors) can occur in some people, especially after long-term antipsychotic therapy, although this is not well understood.

Prevention

To prevent tremors, inform your doctor about all medications you are taking and seek advice before adding new non-prescription drugs. Use stimulants like theophylline cautiously.

Avoid caffeine consumption to prevent symptom exacerbation. Caffeine is found in coffee, tea, and some sodas and can increase muscle activity, worsening tremors. While not life-threatening, tremors can be embarrassing. Consider joining a support group while waiting for symptoms to subside.

When to see a doctor?

Visit a doctor if you are taking medication that may cause tremors if the tremor severely disrupts your daily activities, or if the tremor is accompanied by other symptoms. The doctor will review your medical history and ensure there is no brain or organ damage potentially causing the tremor, such as thyroid issues, Parkinson's disease, cerebellar problems, or functional tremor (tremor without an identifiable cause).

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