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Friday 25th May 2012

I received such a strongly positive reaction to yesterday’s contribution to Sciencegeist’s ToxicCarnival that I thought I’d have a look for another chemical from plants with an interesting story.

In the interests of full disclosure I’d better say that what follows is very largely based on a page that I wrote for this website soon after I first set it up in 2008. But, the ways in which what should be definitive science have been manipulated to suit interest groups seemed to me to be a good example of what started the ToxicCarnival.

Artemisia absinthium, wormwood, contains a substance called thujone. (See yesterday but don’t ask me why it isn’t called artemine). Wormwood was the essential component of the drink absinthe and the accepted wisdom is that it is thujone that imparts the special properties to that drink.

Trying to get at what the true effects of absinthe drinking in the first three quarters of the 19th century were is not easy because, as we’ll see, there are questions to be asked about the typical strength of the drink and there is not even a consensus about what the effect of pure thujone is.

The ‘evidence’ presented for a particular effect is likely to be coloured by the point of view of the presenter. Thus, it may be that the campaign against absinthe in the late 19th century was biased by an unholy alliance of prohibitionists with the French wine industry, anxious to recover the market share lost during the outbreak of grape phylloxera that began in the middle of the century. For the wine growers, it was important to find grounds for attacking absinthe which did not rely on the inherent harm potential in all alcohol consumption.

These days, it seems the majority of those saying that absinthe is not the demon it was made out to be either have a financial interest in absinthe sales or are avid absinthe drinkers. Then there are those who want absinthe to appear to be capable of delivering a ‘legal’ high so as to sell it to people who would not consider using illicit psychoactives, especially cannabis.

Though those two points of view are opposing, they both see benefits in suggesting that absinthe today is no different from what the great artists are alleged to have drunk in France.

Absinthe’s bad reputation dates from long before the end of the 19th century so is it possible, from this distance in time, to say if there is any truth in its alleged ability to cause hallucinations and convulsions and the condition described in the 1860s as ‘absinthe epilepsy’?

The suggestion that the effect of thujone results from its similarity to THC comes from a letter entitled ‘Marijuana, absinthe and the central nervous system’¹. The authors started from the point of view that absinthe and cannabis produced similar psychological effects and hypothesised that this resulted from similarities in the molecular structure of thujone and THC which might result in the substances binding to the same receptors in the central nervous system.

It should be stressed that the authors ‘propose [my italics] therefore that both thujone and THC exert their psychotomimetic effects by interacting with a common receptor in the central nervous system’ and conclude that ‘This hypothesis suggests new experimental approaches’. It must also be remembered that this was a short article and not a full scientific paper.

This proposed association between thujone and THC was seized on and, quickly, became the accepted wisdom. Little actual work seems to have been done to test this hypothesis, however, because seventeen years later it was said that ‘The literature on the pharmacology of thujone is, to put it bluntly, second rate’².

The supposed confirmation of the powers of absinthe has been exploited by today’s producers and distributors. ‘Everybody knows’ that 19th century absinthe was a very dangerous substance so the pitch is to show that modern absinthes are ‘as strong as the legitimate Absinthes of the 19th century’. That claim is worthy of further examination.

The nature of the action of thujone was described in 2000 when it was concluded that thujone can greatly disrupt the nervous system and damage the brain’s self-control mechanism producing epilectiform convulsions, hallucinations and delirium.³ But, did mid-19th century absinthe contain enough thujone to produce these effects?

A typical thujone level in 19th century absinthe has been said to be 260 mg/l.⁴ It is believed that level was determined by replicating old recipes for absinthe and measuring, or calculating, the thujone level. These postulated levels have been challenged by researchers who tested samples of absinthe from the 19th century⁵ but their results were then challenged on the basis that thujone deteriorates with time if exposed to UV and the low levels of thujone measured were not a reliable indicator of the original strength. The authors response to this was to demonstrate that the green bottles used for absinthe would have prevented UV attack⁶.

The samples tested by Lachenmeier et al dated from 1895 at the earliest to the ban on absinthe in 1915 whereas the recipes used to produce absinthe which had the higher thujone levels were from around the 1850s. There is an inherent flaw in assuming that ‘absinthe’ is a definition just as saying ‘beer’ doesn’t give a precise measure of strength or content. By the last decade of the century, grape phylloxera, first seen in France in 1863, had caused considerable damage to the French wine industry and it is possible that absinthe makers revised their formulations to encourage more wine drinkers to sample the spirit.

The question of thujone levels is commercially important. The 260mg/l level reported by Prof Arnold is well above the current European limit of 35mg/l so, to substantiate the claim that modern absinthe is ‘as strong as the legitimate Absinthes of the 19th century’, current producers have to go with Lachenmeier et al and not Prof. Arnold.

Along with the arguments about thujone strength there is the argument about whether absinthe produced unique deleterious effects, ‘absinthe epilepsy’, or simply produced alcoholism in those who consumed it in large quantities. There have also been some suggestions that deliberate adulteration or accidental contamination might have resulted in the production of absinthes that caused the effects ascribed to thujone.

The term ‘absinthe epilepsy’ appears to have been coined by Dr Magnan who, in the 1860s, had some 250 absinthe abusers in his care and based his new term both on his observations of these patients and by experimentation on animals. In 1895, the Royal Society published a paper detailing experiments on cats to determine the progress of absinthe epilepsy. In a paper delivered to a conference on eugenics in 1912, Dr. Magnan described in detail the attacks suffered by absinthe abusers and saying ‘it is exactly like an attack of epilepsy’.

A re-examination of his work, in 2009, found that his findings in relation to cats were valid but concludes that it is impossible to know if the thujone levels in commercial absinthe were high enough to produce the effects he saw.⁷

So, there is no dispute about the harm which can be caused by the oil of Wormwood extracted from Artemisia absinthium containing high concentrations of thujone but it seems unlikely that there will ever be a consensus on whether there was sufficient thujone, even in crudely produced absinthe, to carry those effects into absinthe drunk in ‘normal’ quantities. As with so many chemicals, the observed effects are heavily influenced by the position of the observer. 

References

^1.Marijuana, absinthe and the central nervous system. del Castillo J, Anderson M, Rubottom GM. Nature. 1975 Jan 31;253(5490):365-6.
^2.This and that: an artefactual alkaloid and its peptide analogs B. Max Journal: Trends in Pharmacological Sciences - TRENDS PHARMACOL SCI , vol. 13, pp. 341-345, 1992
^3.α-Thujone (the active component of absinthe): γ-Aminobutyric acid type A receptor modulation and metabolic detoxification Höld, Sirisoma, Ikeda, Narahashi, and Casida PNAS April 11, 2000 vol. 97 no. 8 3826-3831
^4.Vincent Van Gogh: Chemicals, Crises and Creativity' Professor Wilfred N. Arnold Published by Birkhauser Boston Inc 1992
^5.Chemical Composition of Vintage Preban Absinthe with Special Reference to Thujone, Fenchone, Pinocamphone, Methanol, Copper, and Antimony Concentrations Lachenmeier, Nathan-Maister, Breaux, Sohnius, Schoeberl, And Kuballa. J. Agric. Food Chem., 2008, 56 (9), pp 3073–3081
^6.Long-Term Stability of Thujone, Fenchone, and Pinocamphone in Vintage Preban Absinthe Lachenmeier, Nathan-Maister, Breaux, Sohnius, Schoeberl, And Kuballa. J. Agric. Food Chem., 2009, 57 (7), pp 2782–2785
^7.Absinthe, epileptic seizures and Valentin Magnan. Eadie. J R Coll Physicians Edinb. 2009 Mar;39(1):73-8.  

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