Every drug has its physical costs. Some more than others. Alcohol, for instance, has no non-harmful dose-- even one glass of wine with dinner is bad for your body-- but many people drink throughout their long healthy lives.

That said, "harmful" drug use in this case likely refers to exceptional harm, perhaps including addiction or overdose.

You can be given, essentially, heroin at the hospital if in extreme pain. Would you consider this to be "non-harmful"? I would.

How do you define "non-harmful"?

I've known a number of senior executives in well known tech companies who are regular users (weekend partiers) of a number of drugs ranging from marijuana to cocaine, heroin and LSD. They are fortunate enough to have enough income to buy quality product, not cut with harmful chemicals.

Given that they lead very successful lives, I think the drug use is not harmful to them currently. Perhaps as they age out of their 40's and 50's the drug use will become more of a burden on their bodies, but there are certainly lots of lifestyle choices that are harmful to one's health that don't include any drugs at all.

Socially and relationships are in serious trouble. If you measure success as in performing in business and don't count the family and children then okay. Drugs harm relationships. Its proven.

People on drugs are emotionally numb and a emotionally numb people make horrible friends and parents. http://cascw.umn.edu/wp-content/uploads/2014/04/SubstanceAbu...

Best I have seen or heard on the effects of drugs on relationships. This is from "Liberal" This American Life.

http://www.thisamericanlife.org/radio-archives/episode/524/i...

The article you linked to is talking about "Substance abuse", but there's a big difference between drug use and drug abuse.

I know many drug users (some legal, some not), but only know of one person who has had a substance abuse problem, and his problem was with alcohol.

I don't know how much cocaine, heroin, or cannabis use is non-harmful, but the amount is certainly larger than none for all three drugs.

About cannabis, you would say that based on what?

Multiple of research studies. The long term harm has been ruled out but short term of days and weeks is shown in multiple of studies in regards to harm to cognitive and memory.