Half of all Dutch people take nutritional supplements, vitamins amongst others. The fact that vitamins can be toxic when taken in overdose is not common knowledge. There is no evidence that taking vitamin supplements without medical indication improves the health of people with a varied diet. Many are seduced by health claims to use vitamin supplements, unaware of the fact that the evidence for effectiveness is lacking, let alone of the risks of overdosing. In this article, we describe the known toxic symptoms of each vitamin. Furthermore, the toxic doses were indexed against the available dosage, both through regular pharmacies and online. The doses reported to have toxic effects have not always been properly studied. Consequently, toxic doses may be higher or lower than the doses mentioned in this article. The vitamins for which no toxic effects have been described are not automatically safe in every dosis, considering the lack of systematic research into the potential toxicity of vitamins.