According to the Substance Abuse and Mental Health Service's Treatment Episode Data Set, in 2020 in the US there were 139,481 admissions to treatment with marijuana reported as the primary substance out of the total 1,416,357 admissions to treatment in the US for those aged 12 and older for all substances that year.

By comparison, in 2010 in the US there were 358,034 admissions to treatment with marijuana reported as the primary substance out of the total 1,928,013 admissions to treatment in the US for those aged 12 and older for all substances that year.

Source

Substance Abuse and Mental Health Services Administration, Center for Behavioral Health Statistics and Quality. Treatment Episode Data Set (TEDS): 2020. Admissions to and Discharges from Publicly Funded Substance Use Treatment Facilities. Rockville, MD: Substance Abuse and Mental Health Services Administration, 2022.