Although, I cannot comment personally on what employment chances are after serving in prison, I can state with confidence that having a single, felony drug conviction [0] doesn't automatically result in a denial of employment all of the time.

The largest, single reason which I could see as an automatic rejection for chances of employment is the prior criminal history [1]. It's much easier to explain (and look past) a single offense, versus multiple offenses - especially if they're all in the same vein.

My most recent major job search a few years ago (Texas and Florida, ~8 years post-conviction) was basically 50/50, in terms of offers of employment after criminal history was disclosed. The irony is that the majority of potential employers who asked for details were the ones that sent the job offers.

I know that no two situations are exactly the same (I'll provide details if you want them), but hopefully this is proof that there is light at the end of the tunnel.

[0] Conspiracy to deliver heroin (4-14 grams) & and V.O.P. (dirty urine). [1] https://news.ycombinator.com/item?id=14017760