Harmine is a beta-carboline present in medical plants such as Peganum harmala that have been used traditionally as anticancer therapy. In this study, the aim was to examine if it really does have an effect on cancer and if so, mechanism of action. To do so several earlier studies on the subject have been examined. The result is promising but there is still a lot to study on the subject. Harmine really does inhibit tumour growth. It has been tested on both cellcultures and mice and has proven to decrease tumourgrowth significantly with little effect on normal cells. There have also been studies were harmine has been modified to be more efficient and less harmful. One way to make Harmine more effective is to put a 2-amino-2deoxy-D-glucose on the molecule. Since the cancer cell uses a lot of energy for its growth a big proportion of the medicine will end up here. Another way is to attach a methionin-group to it. This is also taken up exccessively by the cancer cells. Substitution in different areas may reduce it’s toxicity; Substitution with a formiat at R3 for example decreased its toxicity so that no side effects were seen in the mice in the study whereas harmine in large doses gave neurotoxic symptoms. Harmines antitumour activity seems to be due to several mechanisms of action. For example a higher level of p53 has been observed efter treatment with harmine. P53 has been called ”the guardian of the genome” because of its role in preventing genome mutation. In some studies a decrease in vascular endothelial growth factor (VEGF) has also been seen. This is an important factor for the growth of new vessels toward the tumour-site. A reduction in COX-2 has also been seen. Inhibition of COX-2, for example by NSAID, is associated with lower risk for coloncancer. A fourth possible mechanism of action could be a decrease or inhibtion of CDKs/Cyklins wich are necessary for the cellcycle-progression. Although a promising substance, there is still a lot to study. It would be interesting to se comparations to established drugs on the market and also what the long term side effects of Harmine could be. The studies so far have only been done under a short period of time, i.e., weeks or months.