The US Dept. of Justice's Bureau of Justice Statistics reported that on Sept. 30, 2019, there were a total of 158,107 sentenced people in federal prisons in the US. Of those, 73,210 people (46.3% of the total) had as their most serious charge a drug offense. According to BJS, that figure "Includes trafficking, possession, and other drug offenses. More than 99% of federal drug offenders were sentenced for trafficking."
E. Ann Carson, PhD. Prisoners In 2019. Washington, DC: US Dept of Justice Bureau of Justice Statistics, October 2020, NCJ255155.