Does a Laboratory Blood-Viscosity Finding Establish Cannabis-Related Clotting Risk?
Adding cannabinoids to collected blood altered its laboratory flow properties, but that experiment did not establish a person’s risk of a clot or stroke after cannabis use. Blood viscosity, coagulation, and clinical vascular events are different endpoints.
Human specimens, in-vitro exposure
James and colleagues collected blood from 24 healthy adult nonsmokers and added THC, CBD, or cannabinoid-containing extracts outside the body. They measured viscosity, elasticity, and red-cell appearance.
The study used human-derived specimens, but participants did not receive cannabis. Calling it a human cannabis-administration trial would obscure the absence of circulation, metabolism, and other processes present in a living person.
Preserve the endpoint-specific results
Viscosity increased at several tested concentrations. THC and CBD separately did not significantly increase elasticity, whereas the extracts did. The two extract ratios did not significantly differ from each other on those measures.
Red-cell morphology was unchanged at lower tested concentrations and abnormal at higher ones. A summary stating that all concentrations destroyed cells would therefore be inaccurate. The paper’s broad conclusions should be read alongside its more specific results.
From flow measurements to a clinical opinion
Viscosity describes resistance to flow; it is not itself a demonstrated thrombus. The experiment did not measure incident strokes, clinical hemolysis, or outcomes in patients with sickle cell disease. Those consequences discussed by the authors are extrapolations requiring additional evidence.
Whole-blood spiking concentrations also cannot automatically be compared with plasma concentrations from other studies. A defensible opinion identifies the matrix, exposure procedure, and measured response before proposing a mechanism. This paper supplies a laboratory hazard signal, not an individual diagnosis, a safe-dose threshold, or proof that cannabis caused a vascular event.
The tested spiking concentrations were 0, 2.5, 25, 50, and 100 ng/mL. Viscosity increases became significant from 25 ng/mL, while cell appearance at 2.5 and 25 ng/mL resembled controls. These are concentrations added directly to collected blood. They are not administered doses, and the experiment does not establish that consuming a specified amount produces the same laboratory conditions.
Related reading: interpreting cannabis-related blood-cell findings.
Primary research
Tameika R. James; Andrea A. Richards; Dwight A. Lowe; Walton A. Reid; Charah T. Watson; Dagogo J. Pepple. The in vitro effect of delta-9-tetrahydrocannabinol and cannabidiol on whole blood viscosity, elasticity and membrane integrity. Journal of Cannabis Research (2022). DOI: 10.1186/s42238-022-00126-z.
