In our previous column (in the February ABT), we reviewed the impact of two key factors that precipitate relapse: (1) priming (introduction of small amounts of the drug), which acts on the mesolimbic dopamine pathway in the brain; and (2) stress, which acts on a variety of neural pathways. As our exploration of addiction and the brain continues, the endocannabinoid system contributes additional pieces of information to enhance our understanding of addiction.

Who ever would have thought that the active ingredient in marijuana, tetrahydrocannabinol (THC), had receptor sites ready and waiting in our brains? The plant that gives us marijuana, Cannabis sativa, has been known for thousands of years. Its psychoactive properties have been used over the centuries and across the world. Once the chemical structure of THC was identified, the research began (Gaoni & Mechoulam, 1964).

There have been three major breakthroughs in cannabinoid research,...

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