The term 'opioids' refers to opiates and other semi-synthetic and synthetic compounds with similar properties. Opiates are a group of psychoactive substances derived from the poppy plant that include opium, morphine and codeine. The term 'opiate' is also used for the semi-synthetic drug diamorphine (heroin), which is produced from poppy compounds. Opioid dependence can cause a wide range of health problems and is often associated with misuse of other drugs (including alcohol). Diamorphine is the most widely misused opiate, and its misuse can lead to accidental overdose. Injecting diamorphine may also be associated with the spread of blood-borne viruses, such as HIV and hepatitis B or C. The mortality risk of people dependent on illicit diamorphine is estimated to be around 12 times that of the general population. Psychiatric comorbidity – particularly anxiety, but also affective, antisocial and other personality disorders – is common among opioid-dependent people.