TS clearance and drug use

[helloworld]

I am a 25 year old engineer for a Department of Defense contractor and have been requested by my employer to obtain a TS clearance. My drug use involved marijuana less than 20 times, over about a two year period, 5+ years ago. Also, some unprescribed prescription drugs (hydrocodone and adderal) over about the same period.

I did not disclose my drug use when I applied for my Secret clearance 3.5 years ago because I was nervous about keeping my job / ashamed. I know it is important to disclose it now.

I am pretty spotless otherwise. With that said, could my drug use and previous non-disclosure affect me obtaining a TS working as an engineer for a DoD contractor?

Thank you