From the Director of National Intelligence and OPM
Live or work in a state where marijuana use is legal under state law? Federal employees need to watch out - a state law exemption from prosecution does not protect the employee from prohibitions of federal law - particularly Executive Orders dealing with employee suitability and national security clearances or access to classified information (including the ability to hold a sensitive position).
OPM contributes a letter to agency personnel offices of May 26, 2015, warning of the danger to employees in suitability or national security actions when drug use or possession occurs, irrespective of state law.
Link to chcoc.gov: Federal Laws and Policies Prohibiting Marijuana Use
DNI adds a government-wide distribution, "Adherence to Federal Laws Prohibiting Marijuana Use," attached as a PDF to the OPM letter.
MSPB recently offered cautionary comments about state legalization statutes in (what else?) the nonprecedential decision, complete with a separate opinion by Member Robbins, in Johnson v. Dept. of Air Force, DE-0752-14-0091-I-2 (April 2, 2015). (Who says the MSPB doesn't take pains to ensure federal personnel specialists are properly informed through precedential decisions?) Go ahead and read the NPFO, paying attention particularly to the remarks of Board Member Mark Robbins.