This paper explores Canadian professionals’ engagement in licit, illicit, and pharmaceutical substance use, their perspectives on what constitutes professional misconduct and conduct unbecoming in relation to substance use, and the dilemmas they face around self-disclosure in the context of professional regulation and social expectations. The study involved semi-structured, dialogical interviews with n = 52 professionals. Key findings are: (i) professionals do indeed use and have a history of using licit, illicit, and pharmaceutical substances, (ii) there is lack of consensus about expectations for professional conduct of substance use in one’s private life and an apparent lack of knowledge about legislation, jurisdiction of regulatory bodies, workplace policy, and workplace rights, and (iii) professionals use high discretion about personal disclosure of substance use to mitigate risk to public reputation and professional standing. Given the real potential for negative consequences associated with self-disclosure of substance use, professionals modify their use to be more consistent with perceived social standards and/or protect knowledge about their use from public disclosure. This can perpetuate assumptions that substance use by professionals is “unbecoming” and risks basing decisions and policies on incomplete and inadequate knowledge. Societally, classist ideologies that position professionals as distinct from non-professionals are reified.