I've been a meth user for over 20 years, well 23/24 years was when I first had access to amphetamines (meth came later in the 90s for/to me). For probably almost a decade I had used meth on most weekends, sometimes all week plus had 1-2 week binges of no sleep etc. Looks wise, I've never looked different as I always ate, looked after myself 'right' when doing meth. I never brushed too much (as that can be as bad as not brushing or worse depending how much brushing when on meth, plus also eating fruit etc before brushing is 'bad')
I haven't been using meth for a few years due to my motorbike injury, plus I stopped being 'full on' with my motorbike since riding a bike brings on more rushes and fun than using (any) substance

Plus you can wake up early and do it all again :D For once I LOVED the sun coming up, it was time to don the leathers and ride, as opposed to "quick, CLOSE the curtains so we can keep partying or time to sleep" heh. So, it's not just being on a substance will stuff up your looks, the people in those typical mugshots are dickheads on meth. They don't take care of themselves with regards to their looks or hygiene. So in the immortal words of Bill Hicks, "Fuck them. Who cares, they're dickheads. They don't deserve our sympathy"
So, if/when on drugs, remember to keep up the personal hygiene and take care of your diet. I supplement with spirulina (lots) when on meth, plus alpha-lipoic acid (anti oxidant, known as ALA) and eat fruit in stages, sometimes having to force it down if my throat doesn't agree with me eating.
*edit*
Oh, also after like 15-20 years of meth use, I looked like 5-10 years younger than my age, MANY people spun out when I told them I was 30/mid 30s, they were going "No way, 20s for sure!). Anyway, gotta go! We're off to a baby clothes warehouse sale!

Bargains!