The invention relates to a method for increasing the therapeutic efficacy of curcuminoids and analogs. More specifically, the invention relates to a method for increasing the therapeutic efficacy of systemically administered formulations that contain curcuminoids and the equivalent therapeutics thereof. The method is characterized in that together with the administration of the formulation the patient is irradiated with visible, and optionally ultraviolet, radiation during a treatment. The invention also relates to phototherapy devices that emit visible radiation over a surface area greater than 0.2 m2 with an irradiance of more than 2 mW/cm2, the devices being suitable for use in the treatment of proliferative diseases, particularly moderate-to-severe psoriasis or tumor processes.