Study: Marijuana may sabotage pregnancy: "Marijuana's active ingredient may thwart pregnancy, a new study shows. The key ingredient -- tetrahydrocannabinol (THC) -- may make it hard for a fertilized egg to implant in the womb, says the study in The Journal of Clinical Investigation. Vanderbilt University's Haibin Wang, PhD, and colleagues studied mice, not people. But they write that their findings have 'high clinical importance' for women. The bottom line from Wang's study: If you're trying to get pregnant, abstaining from marijuana may be important for pregnancy success. Of course, marijuana isn't legally available in the U.S. But it's 'still one of the most widely used illicit drugs in the world, and often by pregnant women,' write Wang and colleagues."