Marijuana, also known as cannabis, consists of dried leaves, stalks, flowers and seeds of the Cannabis sativa plant. 1 ∆9-Tetrahydrocannabinol (THC) and cannabidiol are the primary active components in cannabis and are thought to act on cannabinoid receptor sites CB1 and CB2 to produce psychoactive effects on mood, perception and psychomotor performance. Cannabis plants contain over 60 cannabinoids, which act additively, synergistically, or antagonistically with THC and cannabidiol, modifying the drug’s effects. 1,2 To determine whether legalising marijuana could provide adequate funding for addiction services, this paper discusses available literature pertaining to the financial benefits, health implications and societal impact that legalisation has, paying particular attention to Colorado, USA, where the effects of legalisation can be observed and used to estimate the effect it would have in Ireland.