The addiction is a brain disease with severe medical consequences. Today, all people in the world are exposed to and use a variety of drugs of abuse. The most harmful of them are nicotine, alcohol, heroin, cocaine and 3,4-methylenedioxymethamphetamine (i.e., Ecstasy, or MDMA). If the 60's were the epoch of psychedelic 'culture', the 70's of the epidemic use of heroin, the 80's of the diffusion of human immunodeficiency (HIV) virus infection between drug addicts, the 90's of the popular use of the club drugs and cocaine, the new millennium is characterised by the trend of using several different drugs of abuse concurrently. In the last years the phenomenon of poly-drug use has been prevalent and it is expected to continue. Several concerns are strictly associated with the poly-drug use. The first is represented by the limits of the treatment strategies today available, the second by the various synergistic and interactive effects on the body of the different drugs of abuse (it is well know the harmful and toxic effects of the combined use of alcohol and cocaine), and the third by the serious medical and psychiatric consequences. This book presents a thoughtful plan for treatment of the substance abuse disorders in the addicted populations, and management of the co-morbid infectious diseases in this patient group.