People with intellectual disabilities (PwID) are at a higher risk of developing challenging behaviours (CB). Despite the poor evidence for the effectiveness of medications in managing CB, they are used widely among PwID (50–63%). The aims of our study were to develop a training programme, SPECTROM for support staff to help reduce overmedication in PwID and carry out field testing of SPECTROM including a process evaluation. We developed SPECTROM using the Experience-based co-design method that included four focus groups and a one-day co-design event. Twenty trainees received SPECTROM training. We used the Management of Aggression and Violence Attitudes Scale-Revised-Intellectual Disabilities (MAVAS-R-ID) and the Psychotropic knowledge questionnaire. A semi-structured interview and a feasibility questionnaire were used for process evaluation. SPECTROM website contains 14 modules, resources, and face-to-face training. MAVAS-R-ID scores showed change in staff attitude to ‘medication management’ domain was statistically significant (p < 0.05). Psychotropic knowledge questionnaire showed statistically significant post-training improvement in correct responses (p < 0.05). Process evaluation data showed that SPECTROM was acceptable, applicable, practical, and relevant to staff practice, and helped to improve self-reflection, knowledge, and support to PwID. SPECTROM is a useful training that helps to change the support staff’s attitude toward CB and improve their knowledge of psychotropic medications.