substances other than alcohol (see Chapter 8). The purpose is to introduce the reader to the wide variety of substances that are abused by explaining why people may use them, why the use can be harmful and broadly how this is managed. Liaison psychiatry is the bridge between inpatient care and community care and this complex relationship is demonstrated herein when discussing the management of these cases that require the input of a variety of clinicians. The substances detailed are further subdivided to cover background information, acute intoxication, toxicity, withdrawal states and other management advice. ‘Top tips’ are included where appropriate, which are practical considerations to make based on day-to-day experience working in the field.

An evolutionary perspective on drug use and addiction poses two primary questions that complement the proximate models of mainstream medicine. These are: why are humans motivated to repetitively seek out and consume non-nutritional substances, and why do plants (which are the sources of the majority of such chemicals) manufacture substances that can alter the functioning of the human nervous system? We propose that these questions can have a real bearing on our understanding of the phenomena of abuse and addiction that complements models of proximate causation. The evolutionary perspective recognises that addiction can only arise through the interaction of substances with evolutionarily ancient systems designed to promote the pursuit of rewards associated with increased fitness in the ancestral environment. Thus, neglecting the phylogenetic history and function of such systems necessarily results in an incomplete understanding of this phenomenon. Evolution can also help us to understand human uniqueness and especially the role of cumulative culture and gene–culture co-evolution in shaping the human body and mind. Hence, the evolutionary perspective enables a deeper understanding of the human vulnerability to substance abuse and addiction. The chapter concludes by considering the clinical and public policy implications of the evolutionary perspective presented.