BACKGROUND: No study has investigated when preventive treatment with lithium should be initiated in bipolar disorder.

AIMS: To compare response rates among patients with bipolar disorder starting treatment with lithium early v. late.

METHOD: Nationwide registers were used to identify all patients with a diagnosis of bipolar disorder in psychiatric hospital settings who were prescribed lithium during the period 1995-2012 in Denmark (n = 4714). Lithium responders were defined as patients who, following a stabilisation lithium start-up period of 6 months, continued lithium monotherapy without being admitted to hospital. Early v. late intervention was defined in two ways: (a) start of lithium following first contact; and (b) start of lithium following a diagnosis of a single manic/mixed episode.

RESULTS: Regardless of the definition used, patients who started lithium early had significantly decreased rates of non-response to lithium compared with the rate for patients starting lithium later (adjusted analyses: first v. later contact: P<0.0001; hazard ratio (HR) = 0.87, 95% CI 0.76-0.91; single manic/mixed episode v. bipolar disorder: P<0.0001; HR = 0.75, 95% CI 0.67-0.84).

CONCLUSIONS: Starting lithium treatment early following first psychiatric contact or a single manic/mixed episode is associated with increased probability of lithium response.