The adverse effects of lithium include:
;Very Common (> 10% incidence) adverse effects
* Confusion
* Constipation (usually transient, but can persist in some)
* Decreased memory
* Diarrhea (usually transient, but can persist in some)
* Dry mouth
* EKG changes — usually benign changes in T waves
* Hand tremor (usually transient, but can persist in some) with an incidence of 27%. If severe, psychiatrist may lower lithium dosage, change lithium salt type or modify lithium preparation from long to short acting (despite lacking evidence for these procedures) or use pharmacological help
* Headache
* Hyperreflexia — overresponsive reflexes
* Leukocytosis — elevated white blood cell count
* Muscle weakness (usually transient, but can persist in some)
* Myoclonus — muscle twitching
* Nausea (usually transient)
* Polydipsia — increased thirst
* Polyuria — increased urination
* Renal (kidney) toxicity which may lead to chronic kidney failure
* Vomiting (usually transient, but can persist in some)
* Vertigo
* Weight gain
;Common (1–10%) adverse effects
* Acne
* Extrapyramidal side effects — movement-related problems such as muscle rigidity, parkinsonism, dystonia, etc.
* Euthyroid goitre — i.e. the formation of a goitre despite normal thyroid functioning
* Hypothyroidism — a deficiency of thyroid hormone.
* Hair loss/hair thinning
;Unknown incidence
* Sexual dysfunction
* Hypoglycemia
* Glycosuria
Lithium carbonate can induce a 1–2 kg of weight gain.
In addition to tremors, lithium treatment appears to be a risk factor for development of parkinsonism-like symptoms, although the causal mechanism remains unknown.
Most side effects of lithium are dose-dependent. The lowest effective dose is used to limit the risk of side effects.