Drug addiction is a chronic relapsing disorder that produces a dramaticglobal health burden worldwide. Not effective treatment of drug addiction is currently available probably due to the difficulties to find an appropriate target to manage this complex disease raising the needs for further identification of novel therapeutic approaches. The endocannabinoid system has been found to play a crucial role in the neurobiological substrate underlying drug addiction. Endocannabinoids and cannabinoid receptors are widely expressed in the main areas of the mesocorticolimbic system that participate in the initiation and maintenance of drug consumption and in the development of compulsion and loss of behavioral control occurring during drug addiction. The identification of the important role played by CB1 cannabinoid receptors in drug addiction encouraged the possible used of an early commercialized CB1 receptor antagonist for treating drug addiction. However, the incidence of serious psychiatric adverse events leaded to the sudden withdrawal from the market of this CB1 antagonist and all the research programs developed by pharmaceutical companies to obtain new CB1 antagonists were stopped. Currently, new research strategies are under development to target the endocannabinoid system for drug addiction avoiding these side effects, which include allosteric negative modulators of CB1 receptors and compounds targeting CB2 receptors. Recent studies showing the potential role of CB2 receptors in the addictive properties of different drugs of abuse have open a promising research opportunity to develop novel possible therapeutic approaches.

We acknowledge the financial support of the Spanish MINECO (#SAF2017-84060-R-AEI/FEDER-UE), Instituto de Salud Carlos III-RETICS(##RD16/0017/0020), Ministerio de Sanidad, Servicios Sociales e Igualdad-Plan Nacional Sobre Drogas (#PNSD-2017I068), and the Generalitat de Catalunya-AGAUR ((#2017-SGR-669 and #ICREA Acadèmia2015) and the European Commission-DG RTD (#FP7-HEALTH-F2-2013-602891-NeuroPain) to RM. FEDER funding support is also acknowledged. This work was supported by Red de Trastornos Adictivos, Instituto de Salud Carlos III (ISC-III) and European Regional Development Funds-European Union (ERDF-EU) (RD16/0017/0012), The Basque Government (BCG IT764-13) and MINECO/FEDER, UE(SAF2015-65034-R) to PG. This research was supported by Instituto de Salud Carlos III (RETICS, RD12/0028/0019, RD16/0017/0014 and RD06/0001/1004), Plan Nacional Sobre Drogas (PNSD 2016/016 and 2007/061), Ministerio de Economía y Competitividad (FIS, PI14/00438) and Ministerio de Ciencia e Innovación (SAF2008-01106) to JM