The penalties are suspension of games and fines in weeks. The suspension starts when the letter comes down from the league. These quotes are from the Drug Policy:
Now for those who are still unconvinced here are the rules for implementation of Suspensions:
http://www.nflpa.org/members/main.asp?subPage=Drug+Policy#impb1
This last quote I posted is one paragragh and I made the separations and bold emphasis to make it easy to read.
I do not remember if the 4 game Suspension letter came down last year, I would have to verfiy that.
I. Intervention Program and Discipline for Violations of Its Terms
E. Intervention Stages
2. StageTwo
b. Discipline
(1)Discipline for First Failure to Comply in Stage Two: A player who has a Positive Test or who in the judgment of the Medical Director fails to comply with his Treatment Plan during Stage Two will be subject to:
(a) A fine of four-seventeenths (4/17) of the amount in Paragraph 5 of the NFL Player Contract if the player has successfully completed Stage One; and
(b) A suspension for the period of time to cover four consecutive regular season and post-season (including Pro Bowl, if selected) games without pay if he did not successfully complete Stage One.
(2)Discipline for Second Failure to Comply in Stage Two: A player who has two Positive Tests in Stage Two; or fails twice, as determined by the Medical Director, to comply with his Treatment Plan in Stage Two; or has a Positive Test and fails to comply with his Treatment Plan, as determined by the Medical Director, will incur:
(a) A suspension for the period of time to cover four consecutive regular and post season games (including the Pro Bowl, if selected) without pay if the player was fined pursuant to Section E.2.b.(1)(a) above; and
(b) A suspension for the period of time to cover six consecutive regular and post season games (including the Pro Bowl, if selected) without pay if the player was suspended pursuant to Section E.2.b.(1)(b) above.
Now for those who are still unconvinced here are the rules for implementation of Suspensions:
IV.Imposition of Fines and Suspensions
B. Suspensions
1. Suspension Procedures
1. Suspension Procedures.
During any suspension, the player may not participate with his team in any way (including but not limited to joint press conferences with team officials on or off club premises; provided, however, that the suspended player may see his Treating Clinician for treatment purposes on club property but must vacate the premises immediately following termination of the treatment session with the Treating Clinician), and will not receive any pay, including pay for any post-season game that he misses because of his suspension, except as provided by Article XLII, Section 4 of the CBA.
Notwithstanding the foregoing, if a bye week occurs during a suspension period, the player will receive his compensation for the bye week in equal installments over the remainder of the season after expiration of his suspension for as long as he is under contract with the club that he was under contract with at the time of the commencement of his suspension.
The disciplinary period will begin on the date set in the NFL's notification to the player of his suspension, subject to any appeal.
If there are fewer than the prescribed number of games remaining when the suspension begins, including any post-season games for which the club qualifies, the suspension will continue into the next regular season until the prescribed number of games has been missed.
In all suspensions (other than a banishment imposed pursuant to Stage Three of the Intervention Program), the player shall be eligible to participate in all off-season (not including post-season games) and pre-season team functions, training programs, practices, pre-season games and meetings, up to and including the date of the team's last pre-season game in the next NFL season.
A free agent will serve his suspension as if he had a contract with a Club. The suspension period may be extended if medically necessary, and, if extended, may involve mandatory treatment if required by the Medical Director in his discretion.
http://www.nflpa.org/members/main.asp?subPage=Drug+Policy#impb1
This last quote I posted is one paragragh and I made the separations and bold emphasis to make it easy to read.
I do not remember if the 4 game Suspension letter came down last year, I would have to verfiy that.