In Massachusetts, there is a State policy.
http://www.miaa.net/gen/miaa_generated_bin/documents/basic_module/MIAAHandbook1113.pdf
I'm very surprised you have flexibility in this. Our Baseball coach had to field a team of Freshmen and Sophomores in the playoffs last year when all upperclassmen were caught at a party.
"From the earliest fall practice date, to the conclusion of the academic year or final athletic event (whichever is latest), a student shall not, regardless of the quantity, use, consume, possess, buy/sell, or give away any beverage containing alcohol; any tobacco product; marijuana; steroids; or any controlled substance. This policy includes products such as “NA or near beer”. It is not a violation for a student to be in possession of a legally defined drug specifically prescribed for the student’s own use by his/her doctor. "
Minimum PENALTIES: (also see Rule 32.8 – Ineligible Students)
First violation: When the Principal confirms, following an opportunity for the
student to be heard, that a violation occurred, the student shall lose eligibility for the next consecutive interscholastic contests (regular season and tournament) totaling 25% of all interscholastic contests in that sport. No exception is permitted for a student who becomes a participant in a treatment program. It is recommended that the student be allowed to remain at practice for the purpose of rehabilitation. During the suspension the disqualified student may not be in uniform and his/her attendance at the competition site is determined by the high school principal. All decimal part of an event will be truncated i.e. All fractional part of an event will be dropped when calculating the 25% of the season.
Second and subsequent violations: When the Principal confirms, following an opportunity for the student to be heard, that a violation occurred, the student shall lose eligibility for the next consecutive interscholastic contests (regular season and tournament) totaling 60% of all interscholastic contests in that sport. All decimal part of an event will be truncated i.e. All fractional part of an event will be dropped when calculating the 60% of the season. If after the second or subsequent violations the student of his/her own volition becomes a participant in an approved chemical dependency program or treatment program, the student may be certified for reinstatement in MIAA activities after a minimum of 40% of events provided the student was fully engaged in the program throughout that penalty period. The high school principal in collaboration with a Chemical Dependency Program or Treatment Program must certify that student is attending or issue a certificate of completion. If student does not complete program, penalty reverts back to 60% of the season. All decimal part of an event will be truncated i.e. All fractional part of an event will be dropped when calculating the 40% of the season.
Penalties shall be cumulative each academic year, but serving the penalty could carry over for one year. Or, if the penalty period is not completed during the season of violation, the penalty shall carry over to the student’s next season of actual participation, which may affect the eligibility status of the student during the next academic year. (e.g. A student plays only football: he violates the rule in winter and/or the spring of same academic year: he would serve the penalty [ies] during the fall season of the next academic year) "