Reflecting on the current human enhancement drugs categorisation and new directions to consider

The recognition of human enhancement drugs (HEDs) as a distinct categorisation of substances is a relatively recent phenomenon. HEDs are currently divided into six sub-categories based on their reason for use. Specifically, drugs used to enhance: (1) the structure and function of muscle; (2) weight loss; (3) the appearance of the skin and hair; (4) sexual function and behaviour; (5) cognitive function; and (6) mood and social behaviour. While this provides a useful framework for describing the different types of HEDs, this categorisation would benefit from further development and refinement. Several complexities regarding HEDs were highlighted in the initial categorisation but were not fully explored; for instance, the six categories are not mutually exclusive, some substances are not solely HEDs but may also be prescribed for therapeutic purposes, and psychoactive drugs may also have enhancing effects. The issue is further complicated by the fact that there may not be scientific evidence to support a specific reason for the use of a substance. However, that is not seen as a barrier by consumers, particularly those looking to enhance cognition or sexual performance. This chapter revisits the HED taxonomy, reflect on the issues associated with HED categorisation, and explore the next steps in how we can better understand the use of these substances.