How prevalent is the use of drugs (other than alcohol) to spike food/drinks?

Question

A few years ago, I worked in nightclub security. During my training course,* the instructor told us that it was common for people to come up and claim that they had been spiked with something, but that in 92%† of cases it was just excessive alcohol intoxication.‡

In my experience, a lot of people who believe they have been spiked do not end up in hospital, but some do. Presumably, those who do are screened for drugs (particularly if they wish to press charges), so surely somewhere out there is data showing how many of those screenings come up positive.§

So, my question: What proportion of suspected drug spikings turn out to be just that, rather than overintoxication of alcohol or something else?

Everything I can find on this seems to a) focus on the prevalence of spiking generally and b) relies on self-reporting rather than later toxicology results. For example, this 2016 paper made some waves by claiming that 1 in 13 of its surveyed students reported having been spiked, but is all self-reported. Similarly for this report. Finally, this BBC article says there have been no convictions for spiking in the last five years, which could suggest that most alleged spikings do not show up as such on subsequent tests,| but could also be for any number of other reasons.

*In the UK, security work requires professional training and a government license.

† It may have been higher, but certainly something in the 90s

‡ However, this could be both someone forgetting how much they'd drunk or a case of someone giving them more alcohol than they thought (e.g., double vodka cokes instead of singles), the latter of which would still be considered spiking.

§ Although, of course, it may be hard to tell whether traces of cocaine, to give one example, are the result of the casualty taking it themselves, or having a drink spiked with it, or possibly even both.

| And if someone is just spiked with alcohol, I imagine it would be near-impossible to be able to prosecute this.

Answer 1

AE shared the following paper as a comment: “What's being used to spike your drink? Alleged spiked drink cases in inner city London” (Greene et al., 2007, Postgrad. Med. J) [link]

The paper reports that of 78 study participants (‘consenting patients >18 years of age presenting to a large inner city London emergency department alleging they had consumed a spiked drink within the previous 12 h’), ‘ethanol was detected in 89.7% of participants’ and ‘illicit drugs were detected in 12 (15%) participants’ of whom ‘7 denied intentional exposure’. The authors conclude that ‘overall illicit or medicinal drugs of unexplained origin were detected in 8 (10%) participants [and] unexplained sedative drug exposure was detected in only 2 (3%) participants.’

It's been almost a year since I asked the question, so I think this is likely to be the best answer I get.