In addressing this topic, it will be more comprehensive to go a bit further to include the concept of aetiology in terms of relationship between drug and mental illness. To begin with it, it is necessary to point out that drug abuse, drug dependence or drug addiction is included in the World Health Organisation International Classification of Diseases, and also in the American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders as mental illness. As far back as 1974, the Workshop of the Association of Psychiatrists in Nigeria was the first to call attention to the problem of drug dependence in the country and psychiatrists continue to publish scientific papers in reputable journals. This point is very important and pertinent in this
country where people tend to shy away from accepting that drug abuse is a type of mental illness and seek help from inappropriate agencies. This is particularly so in cases of drug abuse which do not manifest with overt psychotic symptoms but involving drugs with strong addictive attributes like heroin and cocaine. This paper will focus on these.