Yes. I had a friend back in high-school. He was a real nice and good guy. Real good friend too. He smoked pot every single day. He often smoked it multiple times per day (2-3 times). He was very addicted.
Fast forward about 5-7 years and now you can barely have a conversation with the guy. He stutters a lot. He can't concentrate long. Talks real slow and sounds very stupid. He is lazy and got fat.