Depends on the industry and the class of job. In software and white collar work in general it’s almost unheard of. Go farther down the class scale and it becomes very common.

In every bank job I started in NYC I had to take a drug test before I started. Anecdotal... But white collar jobs still do it.

I'm also pretty sure most government jobs require it periodically.

I’ve never heard of a finance industry job that required repeated drug testing. Only at first hire time.

That also makes it kind of obvious that someone is getting ready to jump ship if they stop smoking marijuana for a couple weeks.

If your job requires a security clearance... random testing is a real thing. Same with the medical industry.

If you work in a safety critical, or security critical role, then there is randomized testing as well as pre-employment testing. This can be especially frustrating if you work as a contractor in those industries...

Do they test only marijuana or alcohol, anti-depressant and cocaine as well ?

They test for illegal drug use. So, marijuana, cocaine, and the like.

For driving/piloting jobs, they might add alcohol, but only for a spot test whilst on duty, not general consumption.

So it's not about not being under the influence of something impairing, it's about insurance ? Meaning you can abuse any drug as long as it's legal ?

Were you under the naive impression that those drug tests were for the good of the employees?

USA is not my culture, I need pointers to understand.

No worries.

A lot of our issues stem from our (mostly) Republican Party's "War on Drugs". I could give you a rundown, but the summary section from Wikipedia does a good job.

https://en.wikipedia.org/wiki/War_on_drugs

Yes it is common in most states. This will probably shock people who have never traveled outside the major metro areas of the west coast.

Typically if you drive or operate equipment you are tested regularly. Otherwise you only encounter pre employment tests and that's only found with entry level jobs. Anything above entry level, they are hiring for your past performance and don't care what you need to do during your free time to keep up your groove.

It's never happened to me (I'm in the UK) but I know people who have worked on big public-sector projects where they require that everyone working on it is subject to random drug tests. Network Rail was one example.