Late last year, New Zealand Rugby announced that it was to begin random, out-of-competition drug-testing of players, coaches and administrators – not for drugs that might be used to gain any performance advantage, but for illicit recreational drugs.

The messaging around the announcement was careful. In the words of NZR contracts manager Chris Lendrum, the move was "essentially about the health and wellbeing of our people" and support, rather than punishment.

The reality behind the messaging is more complex. NZR did consider a broader culture-change strategy, like that underway at the Defence Force, which commissioned the New Zealand Drug Foundation to advise on its policies and practices around drug use. (The Defence Force has taken a similar longer-term approach to its sexual violence problem and in 2015 commissioned a review of its own culture from the specialist consultancy Tikai.)

But in the end, rugby went for something quicker and simpler, contracting The Drug Detection Agency, a franchising business whose shareholders include Julie Christie, to conduct its drug testing. The Drug Detection Agency's advisory board includes a franchising lawyer, an accountant, a professional director, a toxicologist and Christie, but no one with direct experience of drug and alcohol counselling.

It is tempting to conclude that NZR is less concerned about pastoral care than with avoiding what happened to Racing 92, the French club now scrambling to manage the PR fallout from its contracted player, New Zealander Ali Williams, getting busted buying cocaine outside a nightclub over the weekend. Williams' arrest compounds the club's problem with another of its New Zealand players, Dan Carter, being arrested for drink-driving two weeks ago. It's notable that almost all the news coverage has noted the club's PR issues and none of it on player welfare.

The irony, of course, is that had Williams bought his coke discreetly and not been a drunk asshole trying to score on the street at 3am, he would have been fairly unlucky to have been picked up in testing, had there been any. Cocaine metabolites are typically detectable in urine for around 48 hours after use. In case of heavy use, or use with alcohol (as per Williams) that could extend to four days, or perhaps a week if use is chronic, but that would be unusual.

Methamphetamine clears detection limits a little more quickly. But, depending on the cutoff value used in testing, cannabis metabolites may be detectable up to a month after use – while impairment is generally back to baseline after three hours . This is, of course, one of the key problems with workplace drug testing: it tends to privilege more harmful drugs which clear the body more quickly.

Which brings us to Prime Minister Bill English's anecdata yesterday about employers who tell him they have trouble finding prospective employees who can pass a drug test. He said:

"One of the hurdles these days is just passing a drug test. Under workplace safety you can't have people on your premises under the influence of drugs and a lot of our younger people can't pass that test."

The problem, of course, is that – with the exception of alcohol – workplace drug tests really don't measure with someone is "under the influence" of drugs. They are more useful in screening for people who are occasional drug users, if that's what an employer wants to do. By the same token, there is no workplace drug test which can tell you whether a potential hire has a long-term problem with alcohol.

I can't find any reliable figures for how many jobs in the economy are subject to either pre-employment or random drug testing (which is to say, almost every news story on the subject originates in a press release from The Drug Detection Agency, which has clear interests in the matter and reports its internal data accordingly). But it seems around 5% of the 90,000 or so tests conducted annually (which corresponds to a lower-than-90,000 number of employees actually tested) return non-negative results, around three quarters of them related to cannabis.

The rate amongst those seeking jobs seems to be much, much lower. After the introduction of sanctions for beneficiaries who failed pre-employment drug tests, the failure rate amongst 8000 beneficiaries tested was 0.27%. Later news reports that the rate of sanctions was growing were statistical bollocks.

Let's be clear: there are sectors in which it is vital that employees not be impaired by drugs. Anything that can be done to improve the terrible workplace safety record of forestry, for example, seems worthwhile. (Although, as Chris Fowlie notes, forestry's enthusiastic embrace of testing does not appear to have improved that safety record.) But we can get an idea of the real-world efficacy of drug-testing in the evidence that the influx of construction workers to post-quake Christchurch created a methamphetamine boom.

Other industries, of course, have no interest in drug-testing their employees. The US tech industry, to take the most notable example, learned many years ago that drug-testing was a good way to lose the race for talent – and while Amazon tests its blue-collar workers, it wouldn't dream of having its coders pee in a cup. There's also the fact that the evidence that drug-testing actually curbs drug use is pretty thin. Further, drug-testing can have unintended consequences – one of the reasons synthetic cannabinoids took off in New Zealand was that for years they didn't show up in drug tests.

But let's come back to those rugby players. Two friends of mine have been in the presence of All Blacks who were on party drugs – one was saucer-eyed and somewhat confused down at the Viaduct two days before a test for which he wasn't in the squad and the other, a legend of the game, had a post-season night out dancing with some friends. Young people do that. But neither was causing the danger or distress to others (or putting themselves at risk) in the way that any number of players have through their alcohol consumption.

New Zealand Rugby and other employers might be better served by treating drug use the way they do (or should) alcohol use: be aware of problematic use, test for actual impairment, counsel. News media should stop treating the press releases of directly-interested companies as news. And politicians should stop reaching for the drug boogeyman every time they're in a tight spot over employment.