MEDICAL CANNABIS OR MARIJUANA IMPAIRMENT

What Are the Facts

Does cannabis alone, inhaled eight or more hours before activities
such as driving a vehicle or working with machinery, cause
significant mental or motor impairment that might increase risk to
self or others? This is the question, properly stated, that
legislators should have considered during the session just ended.

Instead, during the 2005 legislative session, Oregon House Bill 2693
passed the Republican-controlled House. HB 2693 would allow employers
to fire--without evidence of impairment--Oregonians who register with
the Oregon Medical Marijuana Program and who use marijuana as
medicine. Fortunately the house bill failed in a Democrat-controlled
Senate committee after heated testimony, but this may be a temporary
reprieve as this impaired piece of legislation will probably be
introduced again in the next round.

Marijuana as Medicine

Cannabis has been used to relieve pain for centuries throughout the
world, including in the US, prior to the Cannabis Tax Act of 1937.
Cannabis-like compounds are called cannabinoids. The cannabinoid that
most affects mental status, the one that has "psychoactive" effects,
is THC, or tetrahydrocannabinol. THC is a highly effective pain
reliever, equal in efficacy to codeine. GW Pharmaceuticals has
performed randomized double-blind placebo-controlled trials showing
that Sativex (a cannabis extract now available in Canadian
pharmacies) markedly improves pain. For more on Sativex, see
Alternatives Magazine Spring 2005 issue:
www.alternativesmagazine.com/33/bayer.html. Perhaps the best summary
regarding pain relief is from the prestigious Institute of Medicine;
"In conclusion, the available evidence from animal and human studies
indicates that cannabinoids can have a substantial analgesic effect."

The Oregon Medical Marijuana Act (OMMA), passed in 1998, states, " .
. . marijuana should be treated like other medicines." Once inside
the body, THC acts identically whether it comes from herbal cannabis
or from synthetic Food and Drug Administration-approved THC (Marinol,
brand of dronabinol). Either way, the major psychoactive cannabinoid
remains THC so let's examine how THC is metabolized and experienced
by the human body.

Marijuana and Impairment

In A Primer of Drug Action, pharmacologist Robert Julian, MD, PhD,
wrote, " . . . absorption of inhaled drugs is rapid and complete. The
onset of behavioral effects of THC in smoked marijuana occurs almost
immediately after smoking begins and corresponds with the rapid
attainment of peak concentrations in plasma. Unless more is smoked,
the effects seldom last longer than 3 to 4 hours."

In the Journal of Cannabis Therapeutics, Franjo Grotenhermen, MD,
wrote, "Pulmonary [lung] assimilation of inhaled THC causes a maximum
plasma concentration within minutes, while psychotropic effects [the
"high"] start within seconds to a few minutes, reach a maximum after
15 to 30 minutes, and taper off within 2 or 3 hours."

In summary, any mental or motor "impairment" is associated with the
psychotropic effects (the "high"), and these effects are equally
associated with pain relief. When the plasma THC levels return to
low-levels at 3 hours and baseline around 4 hours after smoking
marijuana, the high resolves, and so too does any impairment. This is
important: no impairment after 3 or 4 hours from taking THC.

Marinol is available only by mouth but the package insert warnings
should be heeded regardless of whether a person uses Marinol or
herbal THC. These include: WARNINGS: Patients receiving treatment
with Marinol should be specifically warned not to drive, operate
machinery, or engage in any hazardous activity until it is
established that they are able to tolerate the drug and perform such
task safely. This is sound advice.

When a clinician monitors drug therapy--any drug therapy--s/he
educates a patient through careful explanations of procedures (method
of use and expected results), alternative therapies, and risks
involved in using or not using a medicine. There are many
medicines--prescription or nonprescription--that cause drowsiness or
impairment. These include medicine for blood pressure, diabetes,
arthritis, respiratory infection, allergies, mood stabilization, and
pain. Good communication lessens risks of adverse drug reactions.

Whether in a workplace or not, one should avoid impairment when
driving, operating machinery, or engaging in any hazardous activity.
If the goal is safety, there is no substitute for actual observation
of performance because impairment can have many sources.
Non-prescription medicines, acute illness, or sleep loss can result
in impairment. Good communication between employees, supervisors, and
employers lessens risk of impairment at work.

With all of the above in mind, here is the crux of the problem so
ineffectively addressed by the sponsors of House Bill 2693. The
standard urine test for "marijuana" does not test for the
psychoactive "parent drug", THC. It only tests for an inactive
"metabolite" or breakdown product of THC. Even without physical
evidence of impairment, inactive metabolites can be present for weeks
to months after consuming cannabis. Less frequent users clear
cannabis metabolites from their urine faster than regular users. The
US Department of Transportation says, "While a positive urine test is
solid proof of drug use within the last few days, it cannot be used
by itself to prove behavioral impairment . . .". Here, even the
federal government agrees urine drug testing does not prove impairment.

Fact: There is no significant impairment beyond four hours after
smoking herbal marijuana. Even the flight simulator data, often
tortured by prohibitionists to yield whatever results they wish, can
be summarized. Five flight simulator data studies between 1976 and
1991 yield mixed results usually showing impairment up to 4 hours but
no significant impairment at 8 hours or longer after cannabis consumption.

If the flight simulator testing machines are made difficult enough,
then at least one researcher, Dr. Leirer, demonstrated what he called
a carry-over or "hangover" effect up to 24 hours later. Such a
hangover effect is also seen with commonly used medicines or alcohol.
The purported hangover effect is described by Leirer as "very
marginal" and is only detected in tests of "very complex
human/machine performance". Comparable, subtle effects are reported
at very low blood alcohol levels of 0.025% (25 milligrams of alcohol
per 100 milliliters of blood). Even if a hangover effect can be
measured by a researcher in persons using alcohol, marijuana, or
prescription drugs 24 hours after ingestion of a drug, our laws for
alcohol do not consider 0.025% significant impairment. This alleged
hangover effect causes less impairment than the 0.04% level
considered the safe level for commercial motor vehicle drivers and
far less than 0.08%, the standard threshold for drunk driving. In
other words, flight simulator data actually demonstrate smoked
cannabis beyond 4 hours causes no significant impairment by currently
accepted medical-legal standards.

In light of confusing computer flight simulation data, other
researchers study real motor vehicle accidents. In 2002, authors
Gregory Chesher and Marie Longo concluded, "At the present time, the
evidence to suggest an involvement of cannabis in road crashes is
scientifically unproven". However they note this may only reflect the
evolving science since testing for inactive urine metabolites does
not prove impairment.

Because urine metabolites do not indicate impairment, some scientists
measure the parent drug responsible for impairment. Dr. Drummer
measured blood THC levels in fatal crashes in Australia and noticed
an association between high THC levels and risk of traffic fatality
even in the absence of other drugs. Using forensic evidence he
determined whether a driver is "culpable" or responsible for the
fatal accident and correlated it to blood THC levels. Drummer and
colleagues conclude, "Recent use of cannabis may increase crash risk,
whereas past use of cannabis does not".

Even if one supports using parent drug blood THC levels as a marker
for impairment, it remains unclear how to define the gray area about
what is "recent" versus "past" use of cannabis. This is because the
THC level below which there is no impairment varies dramatically
among individuals. Plus, the actual numbers of persons who have only
THC in the blood and are involved in accidents is low so current
studies lack the statistical significance necessary to draw firm conclusions.

Since no culpability for fatal automobile crashes exists below blood
levels of 10 nanograms per milliliter (ng/ml), those concerned about
legislation suggest that any proposed thresholds be above 10 ng/ml of
blood THC. For more information about legislative considerations see:
You Are Going Directly To Jail: DUID Legislation: What It Means,
Who's Behind It, and Strategies to Prevent It by Paul Armentano:
http://www.norml.org/index.cfm?Group_ID=6492

A study using coordination testing showed inevitable failure on field
sobriety testing if blood THC levels were 25 to 30 ng/ml. But, many
failed testing at 90 and 150 minutes after smoking even though plasma
concentrations were rather low. The researchers had the foresight to
conclude that "establishing a clear relation between THC plasma
concentrations and clinical impairment will be much more difficult
than for alcohol". This is because alcohol and THC are chemically
different and are metabolized differently inside the body.

With medical marijuana laws, we need research to show if there is a
correlation between clinical impairment and blood THC levels. Daily
cannabis users (like patients) can have levels as high as 6 to 10
ng/ml without clinical impairment even after 24 or more hours of
abstinence. Most experts think it is premature to make firm
conclusions about the proper threshold of blood THC as a marker for
"Driving Under the Influence".

Summary

There is no scientific evidence showing significant impairment beyond
four hours from smoking marijuana. There is no scientific evidence of
increased risk of motor vehicle accidents beyond four hours after
smoking marijuana. No physician would routinely condone medical use
of cannabis or other sedating drugs at work. But, careful
consideration of the recommendations in the Marinol package insert
for synthetic THC preserves safety and would be consistent with
medical treatment plans for other medicines that can impair. We have
FDA-approved guidelines for synthetic THC and we should use these
same guidelines for herbal THC.

Registration in the Oregon Medical Marijuana Program should never be
sole cause for termination of employment. Medical use of marijuana
within Oregon law should be treated like medical Marinol, medical
morphine, and other medications, both in and out of the workplace. It
is discriminatory to fire an unimpaired worker whose only cause for
job termination is registration with the Oregon Department of Human
Services Oregon Medical Marijuana Program. Let us hope that we won't
see the sequel of House Bill 2693 surface in the Oregon legislature
next session, and if we do, let us work to defeat such misguided and
damaging public policy.