Lithium has a relatively slow onset of action and will take six to ten days to produce a clinical effect in patients who are manic, and six to eight weeks for patients with bipolar depression.16 Lithium is available in 250 mg capsules, and 250 mg and 400 mg tablets.17 The bioavailability of the different formulations of lithium varies widely, therefore if the preparation is changed, careful monitoring is required, particularly if switching between modified and immediate-release formulations.17