When I was in Clinical Psychology program, we did a study on children born with certain genetic defects such as cleft palates. On thing almost all these kids had in common was that their parents were pretty heavy drug users or marijuana users at some point.
People think their drug use is only going to affect them, but they don't realize the potential drugs have for screwing up your DNA and for passing on birth defects. I have since found that not much is out there to let people know this, but also that people who use drugs will do it anyway - no matter what future consequences may be for them.