I read that it's not safe to use poppers and Cialis or Viagra. Is that true?

You read it right.  Poppers both increase heart rate and cause your blood pressure to drop.  Erectile dysfunction drugs like Cialis, Levitra, and Viagra opens blood vessels.  This combination can cause dangerously low blood pressure, resulting in fainting, heart attacks or strokes.  It's mentioned in the warning that comes with the erectile dysfunction drugs, even.