If they wanted to reduce the number of hospital visits from robo they'd sell it in a pure form and publish information about dosage on the bottle. The former would both prevent false alarms and reduce the motivation to do kitchen chemistry to extract the DXM (the process involves ammonia and butane, not exactly safe). The latter would help recreational users judge how much to take, reducing the risk of accidental overdose. They'd still have to do some math of course, and thanks to government schools they're likely ill-prepared for that, but you have to start somewhere...

Here goes the Cough Syrup Police!