In this paper we investigate direct hemp oil application to head hair and the implications on resulting cannabinoid measurements.
Hemp oil products are advertised in health shops for their good source of omega fatty acids 15 . Bosy et al. 16 assessed whether oral consumption of hemp oil would negatively affect existing drug screening protocols. Various oils were screened (THC content of bottled oils was 36.0, 117.5, 36.4, 45.7, 21.0, 11.5 mg/g) and administered to volunteers and their urine measured for metabolite levels. GC-MS analysis determined the amount of THC-COOH in each participant’s urine to be below the confirmation cut-off within a 48 hour cessation period. Similarly to hemp oil, hemp foods are classified as ‘natural foods’ and are commercially available. Leson et al. showed that daily consumption of hemp food can lead to the presence of THC and THC-COOH in urine, but these compounds were below the confirmation thresholds 17 . These authors 16 , 17 suggest that hemp food and oil products do contain cannabinoids but in very low concentrations, and that ingestion of such products should not be deemed as a concern in drug testing. The Cannabis plant has been used in the production of cosmetics through the use of hemp oil and cannabis extracts 18 . An evaluation of Cannabio® shampoo revealed levels of THC, CBD and CBN, three constituents that indicate cannabis exposure 19 . However, normal hygiene practice using the cosmetic produced no positive results in hair. Extreme use could generate positive results for CBN and CBD but not the primary constituent, THC.
Cannabis Sativa is a plant species of Cannabis. In addition to its recreational use as a drug of abuse, the plant has widespread alternative uses including the production of food, cosmetics (hemp), textiles and medicinal applications 1 . When toxicology laboratories are required to investigate past exposure to cannabis, analysis of hair can provide powerful evidence. The compounds usually targeted for hair analysis to identify cannabis exposure are: Δ(9)-tetrahydrocannabinol (THC), the main active compound of cannabis, the metabolite [11-nor-Δ(9)-tetrahydrocannabinol-9-carboxylic acid (THC-COOH)] and two cannabinoids (cannabinol (CBN) and cannabidiol (CBD)) 2 . Typically passage of these cannabinoids into the hair includes passive diffusion from blood, diffusion from sweat/sebum or external contamination. One of the key questions to be addressed when interpreting the results of cannabinoid hair analysis is that of proof of consumption. Are the results sufficiently clear to suggest cannabis was consumed, or could the results actually be the result of passive exposure to cannabis smoke, or other mechanisms? Passive exposure is defined by an individual being in an environment that is exposed to drugs, an important public health problem. Cannabis smoke can be inhaled or absorbed into the hair by persons other than the intended smoker/user 3 . Researchers have evaluated second-hand cannabis smoke exposure and the corresponding levels of cannabinoids in biological samples 3 , 4 . Herrmann et al. discovered that in unventilated, confined conditions cannabinoid detection was above threshold and higher concentrations of THC and THC-COOH were found predominantly in the blood, urine and hair 4 . THC and THC-COOH have lower incorporation rates in hair in comparison to other bodily matrices. The low presence of THC may be explained by its weak affinity to melanin while the acidic nature of hair may be the reason for the absence of THC-COOH 5 . Along with the levels of cannabis constituents detected in passive exposure, analysis has been conducted to understand what physiological impact exposure has 3 . Past research has shown evidence of increased heart rate and minor impairments in coordination and memory 4 , 6 , 7 . Identification of THC/CBN/CBD in hair suggests exposure to cannabis, which could be due to low level or infrequent use of cannabis or historic or passive exposure. However, some argue that the presence of cannabinoids in hair, especially THC is indicative of repeated or chronic exposure 5 , 8 . The distinction between external contamination and consumption can be difficult for cannabinoid hair analysis 9 , and the implication of a positive test result can have significant consequences for the individual involved. THC-COOH is only formed inside the body, and the presence of this gives unequivocal proof of consumption when detected in hair samples. The metabolite has never been discovered in cannabis smoke ruling out environmental contamination 10 . With hair analysis, THC-COOH is detectable at very low concentrations. The drawbacks for detection from this biological matrix are the requirement for expensive instrumentation and sample preparation can be a more time-consuming process when compared to urine 11 . Routine laboratory screening of hair for cannabis varies and includes the detection of cannabinoids and/or THC-COOH 8 . Hemp is a variety of Cannabis Sativa and is closely related to Cannabis with the difference being in the percentage of THC 12 . Hemp is grown for industrial use and found in food, lotions, medicines, clothing and construction materials. Hemp oil is extracted by pressing the seeds from the female hemp plant 13 . The legalisation of hemp has caused controversy. This is because research has shown that the use or consumption of hemp products could have the potential to impact on drug testing for cannabis 14 .
Hemp oil is marketed as an effective cosmetic treatment for hair, with claims that direct application of the oil to hair has moisturizing benefits, can aid hair growth, may protect the hair and aid in damage repair, and the oil may add shine to the hair. These claims are unsubstantiated but there is a substantial number of online retailers selling various hemp oil based products intended for direct application to head hair. The composition of these products range from pure hemp oil, to hemp oil included at a relatively low concentration into shampoos and other hair treatments.
All data generated or analyzed during this study are included in this published article.
The detection of cannabis constituents and metabolites in hair is an established procedure to provide evidence of exposure to cannabis. We present the first known evidence to suggest that applying hemp oil to hair, as cosmetic treatment, may result in the incorporation of Δ 9 -tetrahydrocannabinol (THC), cannabinol (CBN), cannabidiol (CBD) and in one instance, the metabolite 11-hydroxy-Δ 9 -tetrahydrocannabinol (THC-OH). 10 volunteers treated their head hair daily with commercially available hemp oil for a period of 6 weeks. Head hair samples were collected before and after the application period. Hair samples were washed with methanol and subjected to clean up via liquid/liquid and solid phase extraction procedures, and then GC-MS/MS for the analysis of THC, CBN, CBD, THC-OH and THC-COOH. Application of hemp oil to hair resulted in the incorporation of one or more cannabis constituents in 89% of volunteers, and 33% of the group tested positive for the three major constituents, THC, CBN and CBD. One volunteer showed low levels of the metabolite THC-OH. We suggest that cosmetic use of hemp oil should be recorded when sampling head hair for analysis, and that the interpretative value of cannabinoid hair measurements from people reporting application of hemp oil is treated with caution in both criminology and public health.
Head hair samples were collected from volunteers as described in Methods, and analysed before and after the six week period of hemp oil administration. Results are displayed in Table 1 .
HRMS fragmentation spectrum of cannabigerol (CBG) in positive (A) and negative (B) ionization mode.
CBC has a fragmentation pattern in positive mode very similar to THC so that they are quite undistinguishable ( Figure 6A ). In negative mode ( Figure 6B ), it is possible to discriminate CBC from THC by the ionic abundance of the fragments. Like THC, the molecular ion [M–H] – 313.2171 is the base peak, but unlike THC it generates a higher product ion 245.1544 (25%) deriving from the loss of one isoprene unit. The other two product ions, 191.1068 (55%) and 179.1068 (35%), are higher in CBG than THC, where they are below 10%.
CBG has a very simple fragmentation spectrum in both positive and negative mode. The molecular ion [M+H] + 317.2469 is barely visible and readily breaks to give the only product ion and base peak 193.1225, corresponding to the olivetol moiety with the ortho-methyl group ( Figure 5A ). The molecular ion [M–H] – 315.2394, which is also the base peak, is so stable that the fragments 271.1694, 247.0978, 191.1070 and 179.1068, have very low abundance ( Figure 5B ). These product ions derive from the progressive loss of carbon units of the isoprenoid moiety.
Funding. This work was supported by the UNIHEMP research project “Use of iNdustrIal Hemp biomass for Energy and new biocheMicals Production” (ARS01_00668) funded by PON “Ricerca innovazione” 2014 – 2020 – Azione II – OS L.B). Grant decree UNIHEMP prot. n. 2016 of 27/07/2018, CUP B76C18000520005 – COR 571294. Also, this research work has been partly supported by the funds of the project “Development of a cannabis based galenical preparation” FONDO DI ATENEO PER LA RICERCA ANNO 2017 – FAR2017, Italy ([email protected]@05FA-CANNAZZA_FAR2017-(.20) CUP E53C17000720005).
Δ 8 -THC was not detected in any of the hemp seed oil samples. Although it derives from acid- or oxidatively promoted shift of the endocyclic double bond of Δ 9 -THC and is presented as more thermodynamically stable than its precursor (Hanuš et al., 2016), the chemical environment of hemp seed oil might not be favorable for this isomerization.