The results are variable and inconclusive. Some evidence suggests that FGA-LAIs may improve outcome compared with oral antipsychotics. Methodological issues may partly explain the variable results. Selective recruitment in RCTs and lack of randomisation in observational studies are biases against LAIs, whereas regression to the mean in mirror-image studies favours LAIs. In terms of future research, a long-term pragmatic RCT of an FGA-LAI against an oral antipsychotic, in patients with problematic adherence, would be of value.