Substance use disorders are one of the most highly stigmatised conditions in the western world. Current figures indicate that illicit drug related deaths are the highest they have ever been in the UK. Stigmatising attitudes have been found to act as a barrier to treatment uptake and engagement. This thesis aimed to explore healthcare professionals’ attitudes towards illicit drug users. Part one of this portfolio presents a systematic literature review of healthcare professionals attitudes towards illicit drug use and the treatment of drug users. The findings of the review suggested that healthcare professionals do display stigmatising attitudes towards drug users but that these attitudes may be moderated by factors such as increased contact and the type of drug used. Part two presents an empirical paper that firstly investigated clients and healthcare professionals’ understandings of positive and negative treatment interactions. Secondly, the paper investigated clients’ perceptions of healthcare professionals’ attitudes compared to professionals’ own reports, and the impact of attributions of controllability on attitudes towards a fictional heroin user. The findings highlighted clear discrepancies between clients and healthcare professionals’ understandings of what constitutes a positive and negative treatment interaction. Clients were also found to perceive healthcare professionals as more stigmatising than the healthcare professionals reported being. Attributions of controllability had a variable impact upon attitudes towards the fictional heroin user. Part 3 provides a summary of my clinical experience throughout training. Part 4 presents the assessments that I have completed during training.