Background: Results of discontinuation of antipsychotics in people with intellectual disability are variable and may depend on staff factors. Method: We attempted to taper off antipsychotics in 14 weeks after which participants were free to restart. We investigated the influence of support professionals' feelings towards challenging behaviour, their knowledge of psychotropic drugs and clinicians' judgements of participants' behavioural functioning on whether or not antipsychotics were completely discontinued after 16, 28 and 40 weeks. Results: Of the 129 participants, 61% achieved discontinuation at 16 weeks; at 28 and 40 weeks, 46% and 40% were completely discontinued. Staff's feelings of Depression/Anger towards their client's behaviour, less knowledge about psychotropic medication and clinicians' judgements of behavioural worsening were negatively associated with achievement of discontinuation. Conclusions: To enhance discontinuation off-label drug use, staff's feelings should be explored, their knowledge of psychotropic drugs improved and reasons for clinicians' judgements of participants' behavioural worsening investigated.