Several classes of prescription drugs may be used for recreational purposes and have the potential to induce tolerance and addiction. Benzodiazepines and opioids are currently the major classes of recreationally used prescription drugs [1–3]. Barbiturates, previously much prescribed, have been more or less replaced by benzodiazepines since the 1980s [4, 5]. Central stimulant drugs prescribed for hyperkinetic disorders may also be used for recreational purposes [6]. Recently, reports have emerged on the recreational use of pregabalin, gabapentin and quetiapine [7–9].

The recent rise in opioid deaths in the USA has been ascribed to an increase in opioid prescription [1]. In the UK primary care setting, there has also been an escalation of prescription of opioids between 2000 and 2010 [10]. Though heroin still is the opioid most frequently involved in fatal overdoses in Europe, the proportion of fatalities involving methadone, buprenorphine, fentanyl and tramadol is rising in several countries [2]. In Norway, the number of fatal opioid overdoses has been stable at 250–300 per year for the last 15 years, but the proportion caused by prescription opioids has increased from 30 to 50% [11].

Data on presentations to emergency departments due to the recreational use of prescription drugs are sparse [12]. Though benzodiazepines and zopiclone/zolpidem (Z-drugs) are reported to constitute 18–57% of acute poisonings treated in European emergency departments, most of these cases were suicide attempts [13–18]. Data for the less frequently appearing prescription drugs have rarely been reported, except in a previous study from Oslo encompassing nearly 3000 cases, where methadone had been taken in 2 % of all poisonings, and buprenorphine in 1 % [15]. Furthermore, in a study of recreational drug toxicity at 16 European centres, benzodiazepines were reported in 20% of cases, methadone in 4 %, buprenorphine in 2 %, and ketamine in 2 % [19].

Some patients are prescribed potentially addictive substances by their doctor and then develop an addiction. Others already have substance use problems and take prescribed drugs as a supplement to illegal drugs. Combination of different types of drugs increases the risk of toxicity. When there is a potential for recreational use, legally bought drugs prescribed by a doctor are also traded on the illegal market. However, a large part of the prescription drugs in circulation on the illegal market in Norway is probably imported illegally from abroad [20]. Benzodiazepines constitute the substance of abuse seized third most frequently by the Norwegian police, after cannabis and amphetamines [3]. A total of 1,152,931 benzodiazepine tablets were seized in 2013 [3]. Since 2010 a large part of the benzodiazepine tablets seized are produced in eastern European countries and smuggled into Norway [3]. Nonetheless, prescription patterns also seem to impact on excessive use and overdoses [1, 21, 22]. Hence, knowing which drugs that show up as toxic agents in emergency departments is an important part of the risk assessment when prescribing.