I agree, if you know what to look for and/or if the person fits the profile. But if the person doesn't fit the profile, i.e., a successful businessman, one might write off the tell-tale signs as a personality quirk. For example, a former client of mine, who was also my best friend, had a 15 year coke habit that finally caught up with him and ruined his business and marriage. Looking back, there were little hints that I should have taken as evidence of drug abuse, but that never crossed my mind because he had built a multi-million dollar business and had a wonderful marriage and didn't fit the profile of a cokehead. But then about 18 months before everything collapsed he started missing business meetings and appointments on a regular basis and showing up late to our weekly golf match. Near the end, he put on a lot of weight quickly, took less pride in his grooming and appearance, and became quite edgy and high strung. He had also stolen hundreds of thousands of dollars from his own business. Looking back, I should have none he was a druggie ten years before I realized he was a druggie, which was still months ahead of when everyone else figured he had a substance abuse problem.
All the coke addicts I have ever known have lost weight in such a rapid time that it was incredible. One girl I knew went from 150 lbs to 90 lbs!
A coke addict packing on pounds has to be a rare exception.