I am not very experienced on this but it depends on how long ago this was and how much you had. With simple possession if it was more than 3 years ago and you were under 18 you could qualify under this exemption:
QUOTE
(ii) Exception.-Clause (i)(I) shall not apply to an alien who committed only one crime if-
(I) the crime was committed when the alien was under 18 years of age, and the crime was committed (and the alien released from any confinement to a prison or correctional institution imposed for the crime) more than 5 years before the date of application for a visa or other documentation and the date of application for admission to the United States, or
It is always good to consult with an experienced attorney to confirm.