I am not sure occasional pot smoking makes a difference but heavy and continual use definitely has an effect.
I know a man who has smoked every day for the past 30 plus years. He runs a successful business and provides jobs for more that 12 employees. Makes plenty of money, doesn't cheat on his wife or his taxes, and has been in business for more that 15 years. His behavior and mere existence shows that the stoner stereotype is just that, a stereotype.