Fentanyl’s effects are fast and dangerous. The highly addictive opioid is the deadliest drug threat in American history. It’s linked to more fatalities under age 50 in the country than any other cause of death, including heart disease, cancer and suicide. Here’s how it affects the brain and body: — It only takes 5 minutes for fentanyl to enter the brain when taken orally, said Therese Kosten,…