Many pharmacotherapies to treat addiction have been developed in the past decades, but have often shown modest efficacy or acted on sub-populations of patients (Potenza et al., 2011; Volkow and Skolnick, 2012). Clinical studies also showed reduced relapse rate in patients receiving behavioral therapy (alcohol), and in general individual differences, including genetic vulnerability, need be considered (Heilig et al., 2011).The question of whether novel opioid compounds could lead to more efficient treatments is under intense investigations. Naltrexone, a general opioid antagonist, was the first opioid medication with FDA approval to reduce the level or frequency of drug intake (Pettinati and Rabinowitz, 2006). Methadone treatment, targeting mu receptors, was a pioneering substitution approach to treat heroin addiction, and a recent report describing eight compounds effective in the treatment of alcohol (acamprosate, naltrexone), opioid (buprenorphine, methadone, naloxone) and nicotine (nicotine, varenicline, bupropion) addiction, shows that mu receptors remain a prime target in most successful treatments for addiction (Pierce et al., 2012). Delta agonists may be efficient to limit disruption of emotional responses in addicted individuals (Lutz and Kieffer, 2012). Delta drugs have
