Long-Acting Injectable Antipsychotics (LAIs) are used to overcome non-compliance in psychoses, mainly schizophrenia spectrum disorders. We aimed to summarize available evidence of studies comparing the efficacy of LAIs to placebo or oral medications for Bipolar Disorder (BD) and/or Schizoaffective Disorder (SAD). We searched six databases from inception to 28-March-2018, using the strategy: long-acting antipsychotics AND (bipolar disorder OR schizoaffective disorder OR mania OR manic OR bipolar depression). We included peer-reviewed double-blind comparisons of LAIs for any clinical outcome occurrence in BD, or open mirror studies with same prospective as retrospective assessment periods. We excluded studies reporting on mixed schizophrenia/SAD populations without reporting results separately. The pooled records amounted to 642. After duplicate removal and inclusion/exclusion criteria application, we included 15 studies, 6 double-blind and 9 open, 13 assessing BD and 2 SAD. Depot neuroleptics prevented manic, but not depressive recurrences and may worsen depressive symptoms. Risperidone long-acting injectable was found to be effective in protecting from any mood/manic symptom compared to placebo, but not from depressive recurrences. Add-on or monotherapy paliperidone palmitate in SAD patients protected from psychotic, depressive, and manic symptoms. In patients with BD-I with a manic episode at study enrolment, aripiprazole monohydrate significantly delayed time to recurrence of manic episodes without inducing depressive episodes. LAIs are effective and well-tolerated maintenance treatments for BD and SAD. They showed better efficacy in preventing mania than depression. LAIs may be first-line for BD-I and SAD patients with a manic predominant polarity and with non-adherence problems.