Seriously, they seriously do. There's always someone as qualified as you applying for whatever job. Why would anyone choose someone with a record over someone without, all else being equal? It's a liability that can turn into a headache, so most employers will choose the person without the record.
*Providing the drug use was short lived.
you're ~35 and admit to smoking a buncha weed and maybe some other stuff in your college frat 10+ years ago? not much of a discussion topic, esp. if you've had a steady job, house, family, etc. since then. doesn't have to be short, you could have been called Mikey Pipes for all 4 years of school... just that it was a phase, and it's been long gone.
smoke weed and pop some lsd 1.5 year ago? that could be a problem, esp. if you're still living the same life essentially as then.