The claim that "a fatal dose of fentanyl is two milligrams" is widely cited but is not entirely accurate or evidence-based. This figure often originates from a crude equianalgesic conversion of morphine's lethal dose to fentanyl rather than empirical toxicological data. The actual lethal dose of fentanyl varies significantly depending on factors like individual tolerance, route of administration, and whether the individual has opioid tolerance.
You hear this "2mg" number widely reported by media outlets, police, and even in some peer-reviewed papers, but likely the figure for a non-tolerant adult human is higher. Most acutely toxic would be the intravenous route, with a fatal dose in a non-tolerant adult likely closer to 3mg. Again that is when administered intravenously. Taken orally, like how the original M30's are meant to be consumed, the lethal dose of fentanyl drops significantly due to the very low oral bioavailability of fentanyl, with a lethal dose closer to 10mg+.
So those shock figures reported in the media where they say, "Enough fentanyl was seized to kill 10 million people" always assumes that those 10 million people were lined up and injected with it intravenously. Additionally, all of shocking media reports base the number off of the total mg weight of the M30 pills or street fentanyl powder seized (and assuming both the pills and powder are made of 100% fentanyl), then dividing the total weight by the "lethal" dose of 2mg. So if 10 kilograms of M30s pills are seized, they report it as, "Enough fentanyl was seized to kill 5 million people". And again, this assumes that the entire pill or powder is made of pure fentanyl and that everyone is lined up and given an IV of their lethal dose.
Similarly they say shocking things like "just enough on the tip of a pencil will kill you", when the reality is that most grown adults, even without a tolerance, could lick that tip of the pencil and survive.
This is not to diminish how lethal street fentanyl is, because the facts are clear, fentanyl and it's relatives kill people on a level never seen with heroin. Nor that fentanyl is a potent opioid. But some of the figures reported in the media are way overblown, designed to shock and generate clicks and advertising revenue.
I've actually seen a few news outlets report that the probable lethal dose is 3mg, which is respectable, but they still don't mention that said 3mg must be administered intravenously to cause death.