If you're a first time offender, you might qualify for the U.S attorney office's diversion program, meaning that
if you successfully complete the terms of your probation, you could emerge from the case without a record
of any conviction.
The maximum penalty for possession of marijuana in the District of Columbia is 180 days in jail and/or $1000 fine. However, there are at least 3 ways in the District of Columbia that you can end up without a conviction, depending on the circumstances of the case, your willingness to do certain things (e.g., commiunity service, drug treatment) and your criminal record. An attorney who is familiar with the system should be able to assist you in getting the case resolved. If you get an attorney, make sure that they discuss these different options with you and the government.