Having some experience of an employer who randomly drug tested (not police, so happy to be corrected if they do it differently)
At the start of the test, you get a change to declare if you are on any prescription drugs or have recently taken any OTC medicine (and why). You may need to supply proof, and the test may or may not be deferred depending on circumstances. Opiates, including OTC strength, will show up. As you are not meant to take OTC opiates for more than a few days, this could cause an issue for Steve, because a short deferral to let OTC clear the body, won't cover it.
But he does appear to be on prescription painkillers, which he should declare, and I don't know if the testing would be detailed enough to show if the amounts in the body were in line with the prescription (he appears to be taking both prescribed and OTC, and does not appear able to stop)
It's a vulnerability (could lose career if unfit for duty - but surely there are useful roles for medically downgraded staff?) and one I expect the OCG might seek to take advantage of (I'm assuming they would find out via Steph, though of course the other person who knows is Hastings. And Kate will probably find out soon too)