This is achieved by the synthesis of a diverse array of complex bioactive molecules, many of which have potent pharmacological properties in humans (hence the large number of drugs derived from natural products made by plants). The secondary metabolic pathways that lead to such molecules can be harnessed in plants and plant cells to produce drugs on an industrial scale, e.g. by expressing key rate-limiting enzymes in the corresponding pathways or blocking competitive enzymes that siphon off pathway intermediates