The status quo, the widely believed “wisdom” of the day, is always difficult to change, however illogical or wrong it may be. Blood letting had been widely used for 1,500 years before physicians figured out that it was not, after all, the ideal go-to therapy for all ills. In that context, 36 years is not a long time, but that’s how long the aromatherapy community has been under the illusion that oils of rosemary, hyssop, sage and thyme should not be used for people with high blood pressure.
In 1964, Dr Jean Valnet’s book Aromathérapie was published. It was a hugely important publication in the development of aromatherapy, and it had a tremendous impact on my own aromatherapy career. However, the quantity and quality of essential oil research available in the early 1960s was extremely poor. There simply wasn’t very much to go on.
In his book, Valnet lists the above four essential oils as “hypertenseur”, and for each one he gives two references: Caujolle, and Cazal. However, the 1944 Caujolle paper he cites is actually about essential oils of lavender, lavandin and spike lavender, all of which were reported to produce a brief reduction in blood pressure after intravenous injection into dogs. None of the other four oils are mentioned, so clearly, this reference was a mistake.
Caujolle and Franck published two other papers, both in 1945, that Valnet might have in fact be referring to. One was about hyssop oil. Injected iv into dogs, it caused an initial drop in blood pressure and then (since the dose was high enough to induce seizures) blood pressure suddenly increased as the seizures came on, and decreased again when they subsided. This spike in blood pressure was considered to be a consequence of the muscular contractions related to the seizures. Unless used in convulsant doses, hyssop oil is in fact hypotensive. The other paper was about clary sage oil, not sage oil. Injected iv into dogs, it caused a slight increase in blood pressure. This paper also noted that sage oil usually caused blood pressure to reduce. The other reference given by Valnet (Cazal) was a thesis from 1943, which I have not been able to find.