Fentanyl killed more than 20 000 people in the US in 2016. It is 50 times more powerful than heroin and up to 100 times stronger than morphine

Nevada’s plan to use fentanyl has drawn criticism from medics and activists who call the move a dangerous human experiment

A 12-year-old Nevada pupil has shot dead a teacher, critically wounded two classmates and turned the gun on himself at his school.