The term self-harm is used in this guideline to refer to any act of self-poisoning or self-injury carried out by an individual irrespective of motivation.

This commonly involves self-poisoning with medication or self-injury by cutting. There are several important exclusions that this term is not intended to cover. These include harm to the self arising from excessive consumption of alcohol or recreational drugs, or from starvation arising from anorexia nervosa, or accidental harm to oneself.

Self-harm is common, especially among younger people. A survey of young people aged 15–16 years estimated that more than 10% of girls and more than 3% of boys had self-harmed in the previous year. For all age groups, annual prevalence is approximately 0.5%. Self-harm increases the likelihood that the person will eventually die by suicide by between 50- and 100-fold above the rest of the population in a 12-month period. A wide range of psychiatric problems, such as borderline personality disorder, depression, bipolar disorder, schizophrenia, and drug and alcohol-use disorders, are associated with self-harm.