Linalool: the floral terpene of lavender and hemp

Linalool is one of the volatile molecules that give plants their scent. Its PubChem record, the chemical database of the US National Institutes of Health, gives the formula C10H18O. Its 10 carbon atoms place it among the monoterpenes, like myrcene and limonene. It also carries an alcohol group: PubChem, drawing here on the Merck Index, describes it as a fragrant monoterpene alcohol found in the essential oils of many aromatic plants.

The molecule exists in two forms, mirror images of each other. Delegated Regulation (EU) 2017/776, which entered it in the European classification of hazardous substances, gives them two names: coriandrol for the (S) form, known as d-linalool, and licareol for the (R) form, known as l-linalool.

Several handbooks compiled by PubChem describe its smell. One likens it to bergamot essential oil and French lavender, another calls it floral, spicy and woody. To place linalool among the plant's other aromatic molecules, see our article on the role and chemistry of terpenes.

In hundreds of oils. According to Fenaroli's handbook, cited by PubChem, its various forms have been recorded in more than 200 essential oils drawn from herbs, leaves, flowers and wood. PubChem also cites fruits, such as apple, citrus and grape.

Some plants are very rich in it. The values below, taken by PubChem from its sources, refer to the essential oil and not to the whole plant.

It is the d form, or coriandrol, that Fenaroli's handbook records in coriander. In hemp, the order of magnitude changes completely, because the content is measured in the flower and not in a distillate.

Little, and with wide variation. In 2017, Fischedick published in Cannabis and Cannabinoid Research the analysis of 233 samples representing 30 strains, obtained over one year from a single medical cannabis dispensary in California. Terpenes were measured by gas chromatography, with confirmation by mass spectrometry. Extract from its results table, in milligrams per gram of sample (mean per strain):

The highest value, 3.1 mg/g for Gelato, represents 0.31% of the mass. Even in this strain, linalool was not the dominant terpene: Gelato contained 9.1 mg/g of limonene, almost three times as much. In three strains out of 30, linalool remained below the method's limit of quantification, that is 0.4 mg/g. The selections that bear this name, such as #33 or #41, are presented in our article on Gelato.

Variation within a single strain matters just as much. For Og Kush, the mean of 1.8 mg/g comes with a standard deviation of 1.0 mg/g over 10 samples. These measurements also concern THC-rich strains sold in California. They give an order of magnitude, not the content of a CBD flower sold in France.

According to the 2021 review presented below, most data on linalool are preclinical, obtained in animals or on cells. In 2018, in Frontiers in Behavioral Neuroscience, Harada and colleagues exposed mice to the smell of linalool. In two classic behavioural tests, the light-dark box and the elevated plus maze, they describe an anxiolytic-like effect, with no motor impairment. The effect disappeared in mice deprived of their sense of smell. Flumazenil, which blocks the benzodiazepine site of the GABA-A receptor, also cancelled it.

This result concerns a smell inhaled by mice. It says nothing about a flower smoked or vaporised by an adult.

The question of cannabinoid receptors was examined on cells. In 2019, Santiago and colleagues tested six common cannabis terpenes, including linalool, on cells carrying the human CB1 or CB2 receptor. Up to 30 to 100 micromolar, none changed the activity of these receptors, nor the response to THC. β-caryophyllene, tested in the same series, did not act on CB2 either under these conditions, whereas a 2008 study had attributed selective binding to it, as our article on beta-caryophyllene details. The authors conclude that if an entourage effect exists, it does not pass through the CB1 and CB2 receptors. This hypothesis is examined in our article on the entourage effect.

That leaves humans. In 2021, a review published in Frontiers in Psychiatry brought together work on linalool and pinene. It concludes that the evidence is mostly limited to preclinical studies and that well-designed clinical trials are lacking. Its authors see in them leads for future research. None of these studies therefore makes it possible to attribute an effect to the linalool of a CBD flower.

Delegated Regulation (EU) 2017/776 entered linalool in Annex VI of the CLP Regulation, under index number 603-235-00-2. It is classified there as Skin Sens. 1B, that is a category 1B skin sensitiser, with the GHS07 pictogram and the hazard statement H317, the one for substances that may cause an allergic skin reaction.

The form of the molecule weighs on this risk. In 2010, in Contact Dermatitis, Christensson and colleagues point out that pure linalool is not allergenic, or only very weakly, but that it oxidises on contact with air and that its oxidation products can cause contact allergy. Tested at 6% in 3,418 consecutive patients seen for dermatitis, oxidised linalool gave a positive reaction in 5.3% of them. These patients do not represent the general population.

In cosmetics, linalool appears in Annex III of Regulation (EC) No 1223/2009, entry No 84, under the name "Linalool". Its presence must be indicated in the ingredient list once its concentration exceeds 0.001% in a leave-on product and 0.01% in a rinse-off product. Regulation (EU) 2023/1545 lengthened this list without replacing the linalool entry. Its recital 6 recalls that the Scientific Committee on Consumer Safety confirmed in 2012 that the allergens already listed, linalool included, should remain, and identified 56 others, detailed in our article on allergens in CBD cosmetics. This obligation concerns cosmetics, such as a balm or a massage oil, and not a flower.

On the food side, linalool is on the Union list of flavouring substances, adopted by Implementing Regulation (EU) No 872/2012, under number FL 02.013. The Joint FAO/WHO Expert Committee on Food Additives (JECFA), which gives it number 356, found at its last evaluation, in 1998, no safety concern at current levels of intake for use as a flavouring. It maintains a group acceptable daily intake of 0 to 0.5 mg per kilogram of body weight, set in 1979 and expressed as citral. This authorisation covers an aromatic use. It says nothing about any effect on health.

The certificate of analysis of a CBD flower deals first with cannabinoids. Linalool only appears on it if the laboratory also measured terpenes, in milligrams per gram or as a percentage of the mass. Below the method's limit of quantification, the result is only recorded as lower than that threshold. In the 2017 study, this was the case for three strains out of 30, with a threshold of 0.4 mg/g.

On the Phytogrammes product pages for Kosher Kush and the 120u resin, the description mentions an opening on linalool and α-pinene. That is an aromatic profile. The terpene list displayed is flagged as an example value, and the page states that no terpene result accompanied by a certificate is published for this lot. For these two lots, the certificate is "Not published" and the laboratory "Not provided". The laboratory page recalls that each product page distinguishes the reference profile from results accompanied by a certificate.

Choosing a flower for its linalool therefore amounts to choosing it for its smell. A figure for its content requires a certificate attached to the lot, dated, that names the laboratory and includes a terpene assay.