Does e juice cigarette pens cause cancer? and is nicotine bad for you?

Not sure: There is no regulation for what companies put in e-cigarettes, so we don't really know what is in there. Therefore, we don't know if it can cause cancer. They have not been around long enough to do the long term studies needed to say either way. Nicotine causes constriction of blood vessels and can be highly toxic, even fatal, at high doses.