It is not possible to have a tolerance that high. Fentanyl is 100x the strength of morphine. Morphine alone is enough to kill you, so it is not possible to need something more than morphine unless you're immortal. Drug traffickers sell fake heroin that's actually fentanyl + 99% baby powder or whatever. When they mismeasure the fentanyl dose, people die. There is no way someone would choose this in a free market where real heroin were available. Fentanyl is 100% the government's fault.