Half of patients who had taken cannabidiol (CBD) oil for four weeks had a positive urine test for THC, although none of them reported feeling high, a small study shows.

Seven of 14 patients taking part in a clinical trial to test the efficacy of CBD to treat anxiety ended up with a positive urine test for a major metabolite of delta-9-tetrahydrocannabinol (THC) even though the levels in the product they were given were far lower than the amount found in legal hemp-derived products.