The present invention relates to an active pharmaceutical ingredient (API) which comprises or consists essentially of cannabidiol (CBD) and one other cannabinoid selected from cannabigerol (CBG), cannabigerolic acid (CBGA), cannabidiolic acid (CBDA), and tetrahydrocannabivarin (THCV) for use as a medicament, and more particularly, for use in the treatment of cancer. These combinations have shown themselves to be synergistic in treating one or more of: breast cancer; liver cancer; lung cancer; pancreatic cancer; melanoma; ovarian cancer; gastric cancer; renal cancer or bladder cancer. Two particularly favored API combinations are: cannabidiol (CBD) and cannabigerol (CBG); and cannabidiolic (CBD) and tetrahydrocannabivarin (THCV).