• Initial adverse effects of lithium therapy include nausea, diarrhoea, vertigo, muscle weakness, and a dazed feeling. These effects often abate with continued therapy. Fine hand tremors, polyuria, and polydipsia may persist.
• Adverse effects tend to be directly related to plasma levels and their frequency increases dramatically at levels greater than 1 mmol/L. For more information see Recognizing lithium toxicity.
• Longer-term adverse effects include:
• Hypothyroidism: there is a small risk that people taking lithium at therapeutic doses may develop clinical goitre, hypothyroidism, or both; the risk appears to be greatest in the first 2 years of treatment. Although this may occur, it should not be a reason for stopping lithium treatment. Levothyroxine replacement is usually indicated. Thyroxine function tests usually return to normal when lithium is discontinued.
• Hyperthyroidism: lithium-associated thyrotoxicosis is rare and occurs mainly after long-term use. It should not constitute an absolute contraindication to lithium treatment. Specialist advice should be sought regarding management.
• Hyperparathyroidism: lithium use has been associated with hypercalcaemia accompanied by elevations in circulating parathyroid hormone (PTH). The coexistence of hypercalcaemia and elevated PTH levels suggests primary hyperparathyroidism. However, significantly greater serum levels of calcium are probably required to inhibit PTH secretion during lithium therapy. The presence of mild hypercalcaemia with elevated PTH is consistent with lithium-induced hyperparathyroidism. Parathyroid surgery is not indicated in this situation, and withdrawal of lithium will result in prompt normalization of serum calcium and PTH levels.
• Nephrotoxicity: a small reduction in glomerular filtration rate is seen in 20% of people taking lithium. In the vast majority of these people this effect is benign. A very small number of people taking lithium may develop interstitial nephritis. Lithium can also cause a reduction in urinary concentrating capacity (nephrogenic diabetes insipidus, with symptoms of thirst and polyuria) which is reversible in the short-to-medium term, but may be irreversible after long-term treatment (greater than 15 years).

[Bocchetta and Loviselli, 2006; BTA et al, 2006; Taylor et al, 2007]

The National Patient Safety Agency has developed a lithium patient information booklet. Copies can be obtained from nhsforms@spsl.uk.com.