This only applies to federal "possession or use", which nearly never happens. Those convicted of "possession or use" are nearly 100% plea down cases when the actual offense was sales, distribution, or manufacturing.
Not true at all - guess what charge you catch if you are caught smoking on a chairlift at a ski resort on Federal land or if you're on a hike in a National park.
Thousands of people every year;
https://www.nydailynews.com/2013/09/16/marijuana-busts-on-fe...