It certainly is a sad reality. But it happens. We had a guy at work who became a menace to the other employees, and the general public, because of his drug use. It started as an occasional doobie on weekends, but gradually grew to pill popping, and eventually playing with crack. One day he a very minor fender bender while driving one of the department vehicles....the biggest, heaviest vehicle in the fleet (in the neighborhood of about 20 tons). No serious damage to either vehicle....paint scrape on the other car's bumper (an older model car with lots of dings and scrapes), and there were no injuries at all. He filled out a police report, and talked the other crew member to keep it under his hat.
This guy was gradually becoming worse and worse, and he needed to get help for his addiction...both to help himself and also for the safety of those around him. I got wind of his fender bender, and, going totally against my grain, I had to 'rat him out'.....never would have even considered it if it hadn't been for the safety issue. I slipped the boss a note, along with some daily paperwork, and made sure he saw it and then shredded it. The boss made and received a few of phone calls around that same time, so no one ever was able to figure out how he found out...they all think it was one of the phone calls. He did contact the PD, and had them fax a copy of the accident report over to him.
When 'crash' returned to the shop, the boss asked about the mishap. The guy nervously explained what happened, and then he was informed that he'd have to take a mandatory drug test....standard written procedure required after all accidents. Since the guy was sure he'd fail the test, he tried quit on the spot, but because he refused the drug test, he was instead fired.
Our employer had always gone out of their way to offer counseling and/or treatment for cases such as this, but the guy refused to ask for the help. He was a good guy and good worker, and a hard worker, but he had become a dangerous worker. We had hoped that he'd plead his case, and ask for treatment and a 2nd chance. I went to his house several times to try to talk him into asking for the 2nd chance, but he preferred to keep the dope, and lose the job. That was about 4 years ago......he panhandles and steals to support his habit. Sad!
That was a fairly extreme case, and not nearly as mild as your friend's case. Maybe some outside support or counseling could help....I'm sure your friend is kicking himself for what's happening, and talking to counselor might help him pick up the pieces and move forward.