Food supplements are used for a variety of purposes, one of which is weight reduction. As excess weight is a long-term condition, some supplements are expected to be used for long periods of time. The long-term use of these dietary supplements makes it highly likely that they will be combined with medications, increasing the risk of food supplement–drug interactions, which are not always known or disclosed, and can lead to serious health problems, as has been observed. This article discusses some of the compounds used as food supplements for weight reduction (green tea extract, Garcinia cambogia, chitosan, quercetin and resveratrol) and the interactions they may cause with some drugs such as: dextromethorphan, buspirone, diclofenac, irinotecan, 5-fluorouracil, cytochrome P450 inducers and inhibitors, statins, orlistat, warfarina, acenocoumarol, fluoxetine, valproate, quetiapine, carbamazepine. This information is expected to be useful for healthcare professionals to detect and intervene on food supplement–drug interactions to ensure the optimization of therapy and patient safety.