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Hey, Man! Like, Pass The Brownies

Over the past ten years, researchers have learned a great deal about cannabinoid (marijuana-like) and opioid (morphine-like) drugs and their interactions. The main psychoactive ingredient in marijuana is THC (delta-9-tetrahydrocannibinol). It produces its behavioral effects by binding to cannabinoid receptors in the brain. Similarly, the main ingredient in opium, morphine, produces its behavioral effects by binding to opioid receptors. Studies have shown that both THC and morphine interact with these receptors to produce, among other effects, an increase in appetite and food consumption in both animals and humans. The findings of these studies have led researchers to investigate the therapeutic value of THC and morphine. Recently, cannabis was approved for cancer and HIV patients, to reduce pain and increase appetite. Just as THC and morphine bind with receptors and increase appetite, other chemicals called antagonists block the effects of THC and morphine and thus suppress appetite and reduce food intake. The antagonist drug rimonabant, which blocks the effects of THC, has been proposed as a medication for the treatment of obesity.

In a recent study, researchers investigated the effects of THC, morphine, rimonabant, and naltrexone (or naloxone) on appetite and food reinforced behavior in rats. They also studied the influence of the interactions between the cannabinoid and opioid receptor systems on food-reinforced behavior. As in prior studies, researchers found that THC and morphine significantly increased the motivation in rats to respond for food, while the antagonists rimonabant and naloxone significantly reduced such motivation. A new finding from the study was that the cannabinoid and opioid systems are interdependent. Researchers discovered that naloxone (the morphine antagonist) reversed the appetite response effects of THC and similarly, rimonabant (the THC antagonist) reversed those effects of morphine. Thus, the effects of THC appeared to be dependent upon the secondary activation of opioid systems and the effects of morphine appeared to be dependent on cannabinoid systems. The findings support the therapeutic use of THC for the treatment of severely reduced food consumption associated with chemotherapy and HIV and the use of antagonists such as rimonabant for the treatment of obesity.

(Solinas, M, Goldberg, SR.: Motivational effects of cannabinoids and opioids on food reinforcement depend on simultaneous activation of cannabinoid and opioid systems. Neuropsychopharmacology 30: 2035–2045, 2005.)

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