Matt is right that NR is usually quite strict on drugs, though there is sometimes some leniency when marijuana is the issue. They will look at the nature of the offense in question, how often you used the substance, and the totality of your application otherwise when reviewing your case and determining whether or not to waive the offense.
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The best bet would be to reach out to your officer recruiter, discuss the situation and he will be able to give you a sense of whether it is something that can be worked around or not. If he is in doubt, he can reach out to the Recruiting HQ and (via the HQ) to NR for a preliminary assessment.