When a company drug tests its employees it says one of two things: 1) They work with heavy machinery or similar so it's reasonable.  2) They're saying, "We don't value you."  Unless the company requires the c-suite to do drug tests too, they think less of you.  

And this is coming from someone who doesn't like weed and thinks it is more dangerous for you than people say it is online.  It's not drugs, it's a red flag.  If they drug test you they'll do other things that devalue you too.