It depends on the actual adjudication policy, which differs by agency. For example, for years it was a well-known but unwritten policy that DoE considered marij

It depends on the actual adjudication policy, which differs by agency. For example, for years it was a well-known but unwritten policy that DoE considered marijuana use within the past 12 months to be exclusory but greater than 12 months ago to be acceptable. There seem to be restrictions on putting this in writing (I think because the actual adjudication manuals are classified) but clearance adjudicators themselves would refer to it as the "12-month rule." The FBI at least used to be notorious for considering any drug use at any point to be exclusory, and I think the CIA generally fell into the same camp. On the other hand some organizations, especially in the IC, seemed to be much more lax about it (but often stricter about things like polygraphs). It is useful to explain a bit about the bureaucracy here: the clearance process consists of the investigation and the adjudication. These are two separate steps and often performed by different agencies. The investigation is often performed by OPM, but DoD switched to doing their own, the FBI always has, and it's acceptable to use private contractors (usually retired insurance investigators) up to the S level in some agencies. The adjudication is much more often performed by someone directly in the issuing agency, and agencies publish their own manuals to which adjudicators work. Although the general grounds for denial of a clearance are in statute, the exact rules of what conduct amounts to what grounds (in other words, the real rules of adjudication) are contained in these manuals.