The method of confirming consumption of a tagged pharmaceutical or nutritional product includes the step of providing a subject with a pharmaceutical or nutritional product which has been tagged with a safe, for example, a plant-based, compound. These compounds may include asparagusic acid or a derivative thereof which is found in asparagus, garlic or an extract of garlic, or 1,8-cineole. Alternatively, the taggant may be dimethylsulfoxide. A subject may be provided with and instructed to consume the tagged product according to a defined protocol. A sample of bodily waste or other biological sample may be collected from the subject and analyzed for the presence of the tag or a metabolite thereof. This method may be used to confirm compliance with the protocol in clinical drug trials or nutritional studies.