Of the 803,200 people on parole in the US at the end of 2021, 22% (approximately 176,704 people) had a drug charge as their most serious offense. The most serious offense was unknown for another 22% of the total.

Source

Danielle Kaeble. Probation and Parole in the United States, 2021. February 2023. NCJ 305589. Washington, DC: Bureau of Justice Statistics.