Short answer: Most likely / bordering on definitely.
During the current downsizing of the Army, every misconduct is being scrutinized. A positive UA is a definite detractor from your career. IAW AR 635-200 and AR 680-35 (ASAP) separation proceeding must be initiated for drug use. If you are a first term Soldier I would say there is a 99.9% chance you will be separated. However, the final determination is up to the Separation Authority, normally the first Colonel in your chain of command.
The only way I could see a Soldier even being considered for retention by the separation authority is if the following were true:
- The Soldier had no other misconduct, ever, and the positive UA was for THC (marijuana) and not a drug such as cocaine or heroin.
- The Soldier has an over abundance of exceptional service which would outweigh the one drug use. Multiple deployments, purple heart, etc.
- Your entire chain of command up to and including your Battalion CSM and CDR recommend retention to the separation authority.
Even having said that, retention is usually not an option for NCOs. It would be near impossible to lead Soldiers, especially if you were to stay in the same unit, after having an article 15 for drug use. Not to mention the negative effect it would have on the morale, good order, and discipline of the unit. NCOs are held (and rightly so) to a higher standard than junior enlisted Soldiers.