In what could be a coup for antimarijuana forces, new research shows that rats exposed to pot's active ingredient at an early age devour more heroin as adults than rats without early exposure. Some experts, though, say the jury is still out on whether the finding is enough to officially label marijuana a "gateway" drug. According to statistics from the National Institute on Drug Abuse, most adults who take illicit drugs start doing so in their early teens. In addition, the earlier kids start smoking dope, the more likely they are to use harder drugs later on. For example, of...