Bipolar disorder has a very high rate of relapse and without drugs 90% of people relapse within 18 months following a manic episode with 70% relapsing after a depressive episode. Even with medication 70% of people relapse within five years. One of the main reasons behind this high relapse rate is that people stop taking their medication - nonadherence. Other patients take some but not all of their medication - partial adherence. Antipsychotic drugs are often used in conjunction with mood stabilizers and these can be given in a 'depot' format which releases the drugs slowly into the system over a period of time and can be administered via a pill, which breaks down slowly, or an injection. This means that people can either receive or take their medication less frequently which helps them to stick to their treatment regime. A review of studies into long-acting antipsychotic drugs for bipolar disorder has found that several trials have shown that depot antispsychotics are effective in reducing relapse in bipolar disorder and that further controlled trials are needed into their effectiveness.
El-Mallakh, Rif S. - Medication adherence and the use of long-acting antipsychotics in bipolar disorder Journal of Psychiatric Practice March 2007, 13(2), 79-85