Hey reach. I'm sure we've all done some damage to our brains. From what I understand, most of our cognitive functions should return to normal after a period of time. It's going to be different for everyone. What you used, how much, how long, your age. There's probably other factors as well. It may take a couple of years or more for some to get back to normal.
If your are really concerned, talk to a doctor.
Don't start using again, it will make it worse.
God bless.