A question for those who started smoking weed relatively young

I have a friend who's only turning 19 and he's been smoking weed every single day for half a year now. He started smoking at around 17-18, but it wasn't done as regularly as now. I myself join him from time to time, however I am very mindful of how often I do it. He's also been diagnosed with depression and has been having severe mood swings ever since this smoking became regular (loses his temper very easily when triggered). His productivity also decreased exponentially. I'm worried and I guess I just want to ask if anybody has had experience with this and how did it affect you in the long run? Thank you in advance!