Short answer: Yes. While telling the truth is absolutely essential all of the time, and I would never counsel anyone to lie or make a false statement, once you admit you lied about drug use in the military context, chances are usually very good that it will spell denial of a security clearance and disciplinary action.
I once prosecuted the discharge of a MSgt (E-7) with 14 years of service who did the same exact thing. He was sent to a discharge board and received an Under Other Than Honorable Conditions Discharge for fraudulent enlistment and false official statement. The regulations required that the case be processed for discharge because the fraudulent enlistment involved drug use. he had many supporters but the discharge board had no choice but to kick him out.
But all this being said, it will ultimately come down to some key factors. First was the drug abuse of the nature which you could have received a waiver at the time of enlistment? Usually marijuana use is waiverable, but other harder drugs are not. Secondly, have you repeatedly denied on other occasions your drug use?
Go get an appointment with the base defense counsel as soon as possible before you make any further statements about this to your chain of command.