Dietary supplements are products that are widely used for instance as energisers or to lose weight. There have been cases reported where undeclared ingredients present in such supplements have caused adverse effects on the health of the user. As there are many different products to choose from, it seems impossible to predict which might contain harmful components and to ban them from the market. Nonetheless, the use of dietary supplements and the experiences of users are shared in online discussions. We describe the development of a search engine to retrieve products associated with certain effects. Upon application we were able to retrieve a list of dietary supplements that are repeatedly associated with excessive effects by users on public fora. The top of the list contains supplements that have previously been banned because they contained undeclared harmful components. The use of the search engine as described here is a powerful method for making a risk-based selection of dietary supplements which can then be analysed for the presence of illegal or other unwanted components.