This guest post is by Richard Bayer, MD, who was the chief filing petitioner for the Oregon Medical Marijuana Act in 1998. He opposes Washington State's Initiative 502, which would legalize, tax, and regulate marijuana. He is concerned that I-502's DUI provision will spread to Oregon. - Eds

It is natural for patients who rely on medical marijuana to desire legalization as I-502 claims. Regrettably, I-502 contains a law called per se Driving Under the Influence of Cannabis, or per se DUIC, that traps innocent drivers including medical cannabis patients.

Currently, the crime requires the state prove impairment. But under I-502, the crime becomes a blood test. Alcohol is an unusual drug because blood and breath levels correlate with impairment. There is no equivalent test for cannabis. Currently, law enforcement proves impairment by field sobriety testing using the laboratory to support the prosecution. This will change with I-502 when having the wrong THC level becomes the crime.

I-502 is a sixty-six page ballot initiative and Section 3 mandates blood measurement of the psychoactive parent compound THC, rather than non-psychoactive metabolite carboxy-THC. (The I-502 campaign has issued a fact sheet in defense of the DUI provision.) Patients who use cannabis regularly develop tolerance to the psychoactive or behavioral effects of marijuana even though blood THC levels may never drop to zero. A major flaw in I-502 is the sponsors failed to test any doctor-approved medical marijuana patients to determine how tolerance affects blood THC concentration.

Doctors' reports from Colorado and Washington State guarantee I-502 will wrongfully convict unimpaired drivers, particularly medical marijuana patients. Impairment from cannabis smoking resolves within four hours but doctor-examined patients show blood THC can remain several times the limits allowed by I-502. Reports of background THC levels from unimpaired patients show that THC can be higher than 15 nanograms.

Background THC that causes no impairment is not psychoactive but will result in convictions with license suspension. This is because THC blood testing on regular users of marijuana cannot accurately determine impairment. Sections 31 through 37 of this lengthy initiative explain I-502's limit of 5 nanograms is only for adults who have blood drawn within 2 hours of the alleged crime, otherwise trace amounts create a zero-tolerance crime—even for patients. Nonusers register several nanograms simply from passive exposure to marijuana smoke.

From a medical perspective, I-502 flunks basic science. The zero-tolerance DUIC for some drivers and an arbitrary THC limit for others snubs medical marijuana patients. No one wishes drivers to be impaired but fairness demands proper medical research before writing a law. Opponents to I-502 believe the current DUIC law is effective and should be enforced, particularly since prosecutors boast a 95 percent conviction rate.

The I-502 campaign quotes Dr. Franjo Grotenhermen who did not test patients in his 2005 paper. When asked for an update in 2011, Dr. Grotenhermen explained, "[T]here is no good correlation between THC concentrations in blood and impairment; blood tests can not accurately show impairment. If you base your test only on THC and take for example a limit of 5 ng/ml, you will miss many occasional users with a lower concentration who are actually impaired, and find several heavy users as impaired who are indeed not impaired."

This means while research on regular users including doctor-approved patients is pending, drivers in Washington State will become medical>guinea pigs to determine whether I-502's DUIC gamble will improve or worsen public safety.

I-502 creates injustice for drivers and betrays medical marijuana patients. Being wrongly convicted of any crime is tragic and causes disrespect for all laws. Please read I-502 in its entirety before casting your vote. We should not harm the innocent while rushing legalization of marijuana. For more information, see