How long is it safe to stay on lithium?
A Debate has long raged about the short- and long-term effectiveness of lithium, the optimal duration of treatment, and the long-term sequelae of use.
The place of lithium as a prophylactic agent in mood disorders was recently addressed in a Cochrane review. This concluded lithium was effective in the long-term maintenance treatment of bipolar disorder, but evidence for its use as maintenance treatment in unipolar depressive disorder was not as robust.
It is unclear what duration of treatment is needed to minimise the chance of relapse. Lithium withdrawal is associated with a significant risk of manic relapse in patients with bipolar disorder (up to 50 per cent in the first three months). A net advantage of lithium therapy probably does not occur until after around two years of treatment, and three years is probably the minimum length of time worth aiming for.
Discontinuation after that will depend on the usual balance of clinical judgments and the dose should always be tapered cautiously over an absolute minimum of four weeks, and preferably longer.
A recent review of the effects of lithium on cognition suggests it has definite, yet subtle, adverse effects on psychomotor speed, and also a trend towards impaired verbal memory. Further research is needed to clarify this issue.
In patients who complain of cognitive changes, it is important to weigh the advantages of prophylaxis against these side-effects.
Paul Mackin is academic specialist registrar in psychiatry, Royal Victoria Infirmary, Newcastle upon Tyne