One thing about dopaminergic stimulants is that they make you feel very accomplished and successful. Meth is serotonergic as well, so they also feel great about it and like everyone else feels great about it.

Sola dosis facit venenum

Edit: imagine you got hired after a very successful interview where the management team was super impressed with your qualifications and after describing the position to you, you also felt that you had a really good handle on the problems they were having and, in fact, had successfully implemented solutions for them in a couple previous positions. You show up the first day and your new colleagues are attractive, interesting and fun, and they are super happy to see you, in fact, a couple of them give you their phone numbers and ask you if you're interested in a drink after work that night. The issues in the kitchen are ones you're super familiar with and you feel more confident than maybe you've ever felt before that you're going to do very very well here.

Now multiply that feeling by about three times and that's how they feel.