Intoxication with alcohol or drugs is the obvious theme of certain charges such as drunk and disorderly conduct or drink-driving. In other offences, intoxication may be a factor that can affect or complicate the issue of criminal responsibility.

Approximately 50% of violent offences and property offences are committed after drugs or alcohol have been consumed, and although consumption may not be directly linked to the offence, there is often a strong association between the two.

Psychiatrists are frequently asked to comment on the effects of intoxication on mental responsibility. Although the legal defences of insanity and diminished responsibility are familiar to psychiatrists, the relationship between intoxication and criminal intent is a complex issue that can raise the possibility of defences against particular offences. This chapter will mainly consider the law in England and Wales. The major differences in the legislation of the other jurisdictions in the UK are given in Box 20.1.

The issues surrounding intoxication and legal defence appear to be addressed in a variety of ways, which might reflect the complexity of the legal arguments. The law has arisen as a ‘compromise’ between acknowledging the effects of alcohol and drugs on mental condition and maintaining criminal liability, for the benefit of society. These are areas into which psychiatrists often stray and may even introduce their own moral code. The legal issues that they should be aware of when considering such a venture are outlined below.

There is a generally held belief that many of the legal issues in this area are centred around a theme of intoxication. This is ill-founded and opinions may be sought about the effects of alcohol and drugs without reliable indices of actual intake. The law is less concerned with more modest and minor consumption, although clinicians are often aware of individual variability and the hazards of estimating consumed quantity from the appearance and behaviour of the defendant at the time of the offence.