Risk of caffeine toxicity associated with the use of 'legal highs' (novel psychoactive substances)

Caffeine has desired stimulant effects similar to but weaker than both classical recreational drugs and novel psychoactive substances. This study was undertaken to determine the caffeine content of a sample of novel psychoactive substances, and we discuss the implications for the management of acute recreational drug toxicity. Six novel psychoactive products ('legal highs') that were not declared to contain caffeine were purchased from different Internet suppliers; one additional product was supplied by the UK police force. Analysis of these products was undertaken using infrared spectroscopy (IR), gas chromatography with mass spectrometry (GC-MS) and liquid chromatography with tandem mass spectrometry (LC-MS-MS) to identify the active ingredient(s) and measure the caffeine content of the product. All seven products, which weighed approximately 1 g each, contained only caffeine as the active pharmacological compound. There was significant variation in the percentage caffeine content (< 2 to 96%), with four powders containing very significant caffeine contents of 87-96%. This study shows that individuals are at risk of significant caffeine toxicity related to the high caffeine content of some novel psychoactive substances. Clinicians, including clinical pharmacologists, need to be aware of this to ensure that the management of acute recreational drug toxicity is appropriate and that over-correction of any hypokalaemia does not occur.