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Background and Objective:
The presence of low concentrations of delta-9-tetrahydrocannabinol (THC) in cosmetics
from hemp oil has raised concerns that the use of these products may cause positive urine
tests for marijuana in workplace drug tests, commonly administered in the U.S. This
study's objective was to estimate a theoretical range of THC uptake rates from the
extensive use of hemp oil cosmetics. They were compared to uptake rates previously found
to cause no confirmed positive urine tests when ingested via hemp food.
Review of the scientific literature found only two relevant experimental studies on the
transdermal uptake of THC. These studies suggest that skin penetration by THC is slow
compared to other, less lipophilic (fat-liking) compounds. However, the high THC
concentrations applied in these studies and other limitations did not allow for
extrapolation of the results to the use of hemp oil cosmetics. Rather, transdermal uptake
factors for THC, i.e. the fraction of topically applied THC that enters the blood stream,
were estimated based on physico-chemical characteristics of THC, known uptake rates of
similar organic compounds, and the consideration of skin conditions.
Procedure and
Project Activities:
Daily THC uptake from the use of hemp oil cosmetics was then estimated for two
scenarios. Both scenarios assumed high, yet conceivable product application rates,
reflecting exclusive use of hemp oil cosmetics. Based on vendor information,
conservatively high hemp oil contents in all products considered were also assumed. Under
the "high-exposure" scenario, a 5% uptake factor for healthy skin was
conservatively assumed. The "worst-case" scenarios further assumed use of pure
hemp oil as massage oil by persons with considerably compromised skin. THC levels in hemp
oil of 5 and 10 µg/g or parts per million (ppm) were assumed for the two scenarios,
respectively.
Results and Discussion:
The exposure assessment indicates that THC uptake, even from the extensive application
of commercially available hemp oil cosmetics to healthy skin, is typically less than 1
µg/day. In case of the highly unlikely full-body application of pure hemp oil with a 10
ppm THC content on partially compromised skin THC uptake could conceivably be raised to 11
µg/day. Even this higher rate is only a fraction of the 450 µg/day of oral THC intake,
found not to result in a confirmed positive urine test for marijuana. Thus, our findings
suggest that even extensive use of hemp oil cosmetics will not cause positive urine tests
for marijuana or even contribute significantly to the THC uptake rates required to produce
a confirmed positive test. In addition, ongoing efforts to reduce THC levels in hemp oil
will further reduce transdermal THC uptake from hemp oil cosmetics.
Conclusion:
The results of this exposure assessment show that specific regulatory action, such as
limiting THC content in product formulation or formulations is not necessary. Limiting THC
levels in hemp oil to 5 ppm appears to provide a sufficient margin of protection from
impacts on health or drug tests by hemp foods and cosmetics. Considering the high margin
of safety, an experimental study is not warranted for the sole purpose of assessing
interference of hemp oil cosmetics with drug testing. However, such a study would provide
useful information on the kinetics of THC uptake as a function of product formulation and
skin conditions.
Acknowledgements:
Funding for this project was provided by the Canada-Manitoba Agri-Food Research and
Development Initiative (ARDI) and Dr. Bronner's Magic Soaps, Escondido, CA.
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