One reason energy-saving technologies don't always make as much a difference as expected is the "rebound effect" (WikiLink)- if something becomes easier/ cheaper/ safer, people will do more/ spend more/ take more risks. If cars use less gas, people may drive farther, since it has become cheaper to travel. People don't feel bad about eating a whole pack of cookies as long as they are "low-calorie" cookies.
The scariest version I've seen of this is right here. Since paramedics have really good medicine to help save people from overdoses, drug users may feel safer in shooting up, putting their lives at risk assuming that paramedics will reach them in time. Alternatively, drug users may mix narcotics with the life-saving substance to do "yo-yoing": shooting up to a high and bouncing back down as the other drug in the cocktail (hopefully) brings you back.