For reference, here is the current FBI drug policy with regard to hiring:


I am not aware of any federal agencies with stricter drug policies than the FBI's. Thus, your use of marijuana six times (provided it's not within the past three years) should not disqualify you.

Drug Policy

The FBI is firmly committed to a drug-free society and workplace. Therefore, the unlawful use of drugs by FBI employees will not be tolerated. Furthermore, applicants for employment with the FBI who currently are using illegal drugs will be found unsuitable for employment. The FBI does not condone any prior unlawful drug use by applicants. The FBI realizes, however, some otherwise qualified applicants may have used drugs at some point in their past. The following policy sets forth the criteria for determining whether any prior drug use makes an applicant unsuitable for employment, balancing the needs of the FBI to maintain a drug-free workplace and the public integrity necessary to accomplish its law enforcement mission.

Criteria

    * An applicant who has used any illegal drug while employed in any law enforcement or prosecutorial position, or while employed in a position which carries a high level of responsibility or public trust, will be found unsuitable for employment.
    * An applicant who is discovered to have misrepresented his/her drug history in completing the application will be found unsuitable for employment.
    * An applicant who has sold any illegal drug for profit at any time will be found unsuitable for employment.
    * An applicant who has used any illegal drug (including anabolic steroids after February 27, 1991), other than marijuana, within the last ten years or more than five times in one's life will be found unsuitable for employment.
    * An applicant who has used marijuana within the past three years or more than a total of 15 times in one's life will be found unsuitable for employment. 

To determine whether you qualify under the FBI's drug policy, please answer the following questions. If you answer "YES" to any of these questions, you should NOT apply for FBI employment.:

   1. Have you used marijuana at all within the last three years?
   2. Have you used marijuana more than a total of 15 times in your life?
   3. Have you used any other illegal drug (including anabolic steroids after February 27, 1991) at all in the past 10 years?
   4. Have you used any other illegal drug (including anabolic steroids after February 27, 1991) more than a total of five times in your life?
   5. Have you ever sold any illegal drug for profit?
   6. Have you ever used an illegal drug (no matter how many times or how long ago)while in a law enforcement or prosecutorial position, or in a position which carries with it a high level of responsibility or public trust?