In this article, I focus on possibly impaired self-determination in addiction. After some methodological reflections, I introduce a phenomenological description of the experience of being self-determined. I argue that being self-determined implies effectivity of agency regarding three different behavioural domains. Such self-referential agency shall be called ‘self-effectivity’ in this article. In a second step, I will use this phenomenological description to understand the impairments of self-determination in addiction. While addiction does not necessarily imply a basic lack of control over one’s (...) life, this can well be the case during certain periods of time or in special situations. Addiction is herein described as an embodied custom—highly effective with respect to changing one’s lived experience—which is learned and developed while becoming addicted. Such a repeatedly performed custom, called a ‘psychotropic technique’, implies deep changes in one’s personal identity and alters an agent’s ‘self-effectivity’. In the closing section, I discuss the possible implications of a phenomenological approach to personal responsibility. (shrink)