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29 September 2004
Ectopic Pregnancies Linked To Marijuana 
Marijuana use may increase the risk of ectopic pregnancies, say researchers at Vanderbilt University. The study, published in the journal Nature Medicine, examined CB1, a cannabinoid receptor that binds the main active chemical for marijuana. In pregnant mice that lacked the gene for the receptor, or in which the receptor was blocked, the embryo failed to go through the oviduct. It also happened in normal mice when the receptor was over-stimulated. The research describes how the CB1 receptor in the mouse regulates muscle contraction to move the embryo down the oviduct. It is not known whether marijuana, which over-stimulates the CB1 receptor can cause ectopic pregnancy in humans. However, "our results raise caution for women of reproductive ages regarding the chronic use of marijuana for recreation or pain alleviation," the researchers said. The current study began with the observation that mice commonly used in genetic experiments often fail to deliver pups, even though they become pregnant. Upon flushing the oviducts, the researchers found the embryos, which for some reason were unable to reach the uterus. This strain of mouse lacks the gene for the CB1 receptor. When the researchers gave a drug that blocked CB1 in normal mice, they observed the same phenomenon - in most of the mice the embryos failed to reach the uterus. The same thing happened when the mice were given an amandamide-like drug to over-stimulate the receptor. Subsequent experiments supported a new concept; the CB1 receptor modulates the release of noradrenaline, which in turn stimulates waves of muscle contraction and relaxation in the oviduct, nudging the embryo toward the uterus. Too much or too little of this "endocannabinoid tone" can result in pregnancy failure. In support of this hypothesis, abnormal muscular contraction that prevents human embryos from reaching the uterus is one known cause of ectopic pregnancy, researcher Sudhansu K. Dey said. Dey said he was also concerned about the potential impact of an anti-obesity drug, now in clinical trials, that suppresses appetite by blocking the CB1 receptor. Such a drug, if approved, would likely be taken by young women of reproductive age. "What will happen if they consume anti-CB1 drugs?" asked Dey.
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