Can Lithium 600 mg Cause Tremors or Akathisia After Six Weeks?
Yes, lithium 600 mg can definitely cause tremors after six weeks of treatment, but akathisia is not a recognized side effect of lithium therapy.
Lithium-Induced Tremor
Tremor is one of the most common side effects of lithium therapy, occurring in 4-65% of patients depending on how it is defined and measured. 1
Clinical Characteristics
- Fine postural and/or action tremor occurs in 4-20% of lithium-treated patients and is classified as an exaggerated physiologic tremor 2, 3
- Tremor may appear during initial therapy and can persist throughout treatment, even at therapeutic serum concentrations 4, 2
- The FDA label specifically lists "fine hand tremor" as a side effect that "may occur during initial therapy for the acute manic phase, and may persist throughout treatment" 4
- At six weeks of treatment, tremor is well within the expected timeframe for this side effect to manifest or persist 4
Severity and Management Considerations
- Tremor is typically described as "an inconvenience rather than a disabling condition" by the FDA 4
- The tremor is increased by high caffeine consumption and concomitant use of other psychotropic agents 2
- Pharmacotherapy for tremor is indicated only in patients with disabling tremor 3
- Treatment options include beta-blockers (particularly propranolol 30-80 mg/day), dose adjustment, changing lithium preparations, or in preliminary studies, vitamin B6 (900-1200 mg/day) 5, 6, 1
When to Worry
- Severe tremor, particularly when accompanied by muscular weakness, lack of coordination, drowsiness, diarrhea, or vomiting, may indicate lithium toxicity and requires immediate serum lithium level measurement 4
- Baseline and regular monitoring (every 3-6 months once stable) of lithium levels is essential 7
Akathisia and Lithium
Akathisia is NOT a recognized adverse effect of lithium therapy. Akathisia is characteristically associated with antipsychotic medications (neuroleptics), not mood stabilizers like lithium 5.
- The evidence shows that propranolol, used to treat neuroleptic-induced akathisia, actually improved lithium-induced tremor as a separate phenomenon 5
- None of the FDA labeling, guidelines, or comprehensive safety reviews mention akathisia as a lithium side effect 4, 2
- If a patient on lithium presents with akathisia-like symptoms (restlessness, inability to sit still), consider other medications they may be taking, particularly antipsychotics, or alternative diagnoses 4
Common Pitfalls to Avoid
- Do not confuse lithium-induced tremor with akathisia—they are distinct movement disorders with different etiologies
- Do not assume all neurological symptoms on lithium are benign—always check serum lithium levels if tremor worsens or is accompanied by other symptoms 8, 4
- Remember that "restlessness" is listed in the FDA label as a CNS adverse reaction, but this is distinct from the motor restlessness characteristic of akathisia 4