Key points

1. We understand online drug monitoring to be the systematic monitoring, via the internet, of trends and developments in the use of substances. During online monitoring, data are systematically collected on search behaviour, the purchase of drugs, discussions regarding the risks or user experiences; the collected data are stored for later analysis.
2. The Trimbos Institute, Netherlands Institute of Mental Health and Addiction, has been performing online drug monitoring since 2013 for our projects to map out trends in the use of (new) psychoactive substances.
3. Online monitoring provides information with a high ecological validity that would otherwise be less easy to obtain. It also offers the possibility of obtaining information about difficult to reach populations.
4. A limitation of online monitoring is that it is not always clear to what population the findings can be generalised. For prevalence estimates, online forum monitoring is therefore not always appropriate. As an early indicator of possible changes in opinions with respect to substances and substance use, it is a potentially effective tool.
5. By combining data from online and offline monitors, a more reliable picture can be gained of the popularity of substances and the associated trends and developments than would be possible using the individual monitors: trends that are detected in one of the monitors can be verified using the other monitors.
6. Online monitoring can be a sensible way to contribute to other monitors to obtain a detailed picture of (trends in) the popularity of substances, including new psychoactive substances. The online monitoring of drug trends will become increasingly important, because it seems that the internet will become an increasingly important medium for the purchase and sale of substances and for the discussions about drugs.