I'd try very hard NOT to OD because all of my problems, read:
MONEY, would be solved... then I could have my cake and eat it too. Fuck. It's way more tempting to overdose when you're a poor piece of shit with no prospects for anything to be honest.

If I won the lottery, I could get high and go out and party and live where ever I wanted to and all that shit... it'd be fucking awesome. So, yeah, winning the lottery would kind of have a more conservative effect on me... I might develop a larger tolerance, but certainly wouldn't be any more reckless.
I'd start my own Hunter S. Thompson-esque drug collection.
For the junkie in me I'd buy myself a fat fucking stack of dope, try to find some original OC 80s or even OC 160s [!!!] (for the novelty factor), Opana 40s, Narcan (just in case), Suboxone, Methadone, Dilaudid... all sorts of everything, really.
Then I'd start down my "TO-DO" list of drugs. The first drug I'd use would probably be DMT. And travel, travel, travel!
And, of course, like others I would invest. Probably in Real Estate or perhaps start my own pot farm in California and try to get a dispensary license, if that's even possible. So I could cook with cannabis -- one of my favorite things to do ever! !
My super duper Accountant would tell me what to invest in, haha. And I'd keep an attorney on retainer, just because!