The opioid system may have a role in pathogenesis of obsessive compulsive disorder (OCD). The association between opioid system, anxiety disorders and drug addiction is not completely understood, however OCD is four times more frequent in opioid addicts compared to normal population. Furthermore, previous case reports and unblinded studies have reported that tramadol (a synthetic opioid) and morphine reduced the symptoms of OCD. There are not studies in the literature that showed improvement of OCD symptoms with heroin use. [Pub Med, MeshPubmed, Ovid, Derwent Innovation Index (ISI Web of Knowledge), Psychiatry index etc.]. We herein report a patient with OCD who started to use heroin for regulation of his blood glucose levels as a consequence of a misbelief. After using heroin, OCD symptoms improved but heroin addiction developed.