He has spoken out briefly on his twitter account:
Late Tuesday night, Allmendinger released a statement through a series of posts on his Twitter feed. "I just want to say thank you first and foremost for all [of you] sticking by me. ... It means more than [you will] ever know," he wrote. "I'm sorry we even have to have this going on. But I promise ... I will do whatever it takes to get to the bottom of this and get back [out] there no matter what."
I agree with Mike, it is very unlikely for him to be able to come back from this situation. But, he is doing all the right things at this stage. He is not arguing with the result, he is co-operating fully & going into the rehab program. And he has said he will do what it takes to get himself clear. He is handling it much better than Mayfield anyway, so he is not burning his bridges at this stage. But in todays ecomonic climate you need either a sponsor behind you or results to back it up. Unfortunately for him, he has neither in NASCAR.
Opti, I wouldn't assume he was a proper regular user. I am not sure how often each driver is likely to be tested throughout the year, but I think it is more likely he used it recreationally every now and then. He probably used it a few times before, done the drug tests and not had an issue, and then BAM, traces in his body and he is done for. I really doubt it was something he used on a race weekend or before driving.