^^^You probably could, given good conections and a nice wad of cash (and in the case of shrooms, the knowledge of chemistry to extract reasonably pure psylocybin), but no sane person ever would. And suicidal people usually prefer downers. There is a lethal dose of everything, including water. As a practical matter, ain't gonna happen. Obviously, you can ruin your whole day at a tiny fraction of the LD-50, and some of the sythetic phychedelics have caused deaths at foolish, but not impractical doses.