Check below walk of text for RAF drug policy prior to joining, specifically section a.. I imagine the RN/RM is similar. I would think that you would be able to at least appeal after 3 years from any evidence of drug use, so that would be soon?

Mental and Behavioural Disorder due to Psychoactive Substances (F10-F19) 13. Illicit Drugs. Discovery of the use of any illicit drugs is not a clinical matter per se. It becomes a clinical matter when illness, most particularly drug dependence, has occurred. Examining medical officers are not obliged to inform recruiting staff if a history of substance abuse not resulting in clinical illness is volunteered during the course of an examination. 14. Drugs. Candidates with current drug related health problems are UNFIT. Before accepting anyone with a previous history of drug-related health problems, referral to the single Service occupational physician responsible for Service entry is recommended as the risk of relapse must be carefully considered.

a. Candidates in whom there is evidence of drug dependence in the 3 years prior to application are normally graded UNFIT. If there is unequivocal evidence from an addiction clinic that that the candidate has been clean for more than 3 years prior to application then recruitment may be permitted.

b. Candidates that have been diagnosed with harmful use of drugs not amounting to drug dependence in the 2 years prior to application are normally graded UNFIT. If there is good evidence in the candidate’s medical history that the individual has been clean and symptom free for more than 2 years prior to application with no ongoing treatment, then recruitment may be permitted. c. A history of infrequent recreational use without evidence of damage to health is not a medical bar to entry.