Why marijuana blood tests fall short of the alcohol standard in determining intoxication – Medical Marijuana Program Connection

CLEVELAND, Ohio — When it comes to enforcing drunken driving laws, police have a battery of tools at their disposal. Field sobriety tests, along with breath, blood, and urine tests for blood alcohol concentrations are well established indicators of a driver’s degree of intoxication.

However, in the case of marijuana, the drug’s unique metabolism makes the question of intoxication – on the road or in the workplace – more complicated.

That’s because tests for drug levels in the blood only tell us whether someone used marijuana in the last several days or even weeks, not whether they are under the influence at the time.

Earlier marijuana use still causes positive blood tests because the psychoactive component of cannabis – tetrahydrocannabinol or THC – sticks around the body in fat cells and is released back into circulation long after the intoxicating effects on the brain have gone away.

The limitations of drug testing have come up as Ohioans vote on a Nov. 7 ballot proposal – Issue 2 – that would legalize recreational marijuana use in Ohio.

Here’s what we know.

What a drug test for cannabis does and doesn’t measure

Tests for cannabis don’t actually measure THC, the component of cannabis responsible for the feeling of being “high.” Shortly after THC reaches the bloodstream it is rapidly taken up in the fat cells of the brain and body, and little remains in circulation to measure.

Instead, as a proxy for THC, a urine test for cannabis measures a product of its…