What's more dangerous - the bute or the burger?
There is reasonable public outrage at possible criminal conspiracies to adulterate meat products with horsemeat, and additional concerns raised about the presence of the anti-inflammatory known as bute.
While not in any way questioning this concern about adulteration with a chemical compound, it is helpful to get a sense of magnitude. When bute was given as a human medicine, it was reported to be associated with a serious adverse reaction in 1 in 30,000 (over a whole course of treatment), but at a dose giving concentrations at least 4,000 times that arising from eating a diet of horse meat - see the excellent information from the Science Media Centre
So making all sorts of heroic assumptions about there being a linear-no-threshold response, we might very roughly assign a pro-rata risk of a serious event as 1 in 100,000,000 per burger.
Compare that with the risk from the meat itself. There is good evidence that red meat consumption is associated with an increased risk of bowel cancer, and specifically a large recent study from Harvard associated a daily habit of 80g (3.5 oz) of red meat with an increased all-cause mortality rate of 13% - I recently showed in this British Medical Journal paper that this was as if, pro-rata, each portion of red meat was associated with ½ hour loss in life-expectancy, around 1,000,000th of a young-adult’s future life.
So my rough guess is that for a burger made out of horse-meat containing bute - or indeed any kind of red meat - the burger itself carries around 100 times the apparent risk of the bute. Even taking into account that the bute reaction would occur quicker than any harm from the red meat, this still is a notable disparity.
Of course I know very well that people, including myself, feel very differently about risks that are chosen as part of daily life, and appear ‘natural’, to those imposed by outside (probably criminal) agencies and involve unnatural substances. I fully respect those feelings, but I still believe some perspective is valuable.