PHYSICIANS UNLIKELY TO EMBRACE MARIJUANA AS MEDICINE

It wasn't just women with breast cancer who were excited last month
when scientists at California Pacific Medical Center Research
Institute showed that a compound found in marijuana may be able to
block the growth of aggressive tumors. This finding also cheered
activists who hope that mainstream medicine will soon embrace
marijuana as a treatment. For a range of reasons, that's extremely unlikely.

Effective medicines can of course be derived from plants. Digoxin
from foxglove, atropine from belladonna and quinine from cinchona are
only a few examples. The marijuana plant likewise contains
potentially therapeutic compounds known as cannabinoids, one of
which, cannabidiol, was examined in the breast cancer study. Other
research has examined tetrahydrocannabinol (THC) - the cannabinoid in
marijuana that is primarily responsible for the plant's psychoactive
effects (e.g., feeling "high," hallucinations, changes in mood). THC
has been shown to benefit at least some patients with a range of
problems, including chemotherapy-induced nausea and the tremors and
muscles spasms associated with multiple sclerosis.

Nonetheless, only a minority of physicians harbor great enthusiasm
for prescribing marijuana cigarettes. Indeed, a survey of almost a
thousand physicians by Brown University researchers showed that
doctors are significantly less supportive of medical marijuana than
is the general public.

Older members of the field remember vividly the era when most
physicians smoked tobacco cigarettes and cheerfully rated Camel their
favorite brand. The tobacco industry built on this foundation with
deceptive advertisements linking doctors with smoking in the public
mind (currently on exhibit at the UC San Francisco library on 530
Parnassus Ave.), which damaged medicine's credibility.

These bitter historical experiences, supplemented by decades of
subsequent research evidence that smoke inhalation of all forms (even
wood smoke) can cause acute and long-term respiratory damage, make
many physicians wary of recommending a smoked medicine. A smoked
plant has the further disadvantage from a medical perspective of not
being pure (e.g., what if the plant had been sprayed with pesticide?)
or of a standardized dose. This exposes the patient to risk of side
effects, and the physician to risk of malpractice.

As the California Pacific research team noted, for example, obtaining
the correct dose of cannabidiol through smoking marijuana would be
virtually impossible. It would also of course cause THC's
psychoactive effects (cannabidiol is not psychoactive), which some
patients find aversive. Will all the therapeutic components of
marijuana one day be available in pure, standardized forms that can
be safely administered without combustion?

Liquid THC, known as dronabinol, has been available by prescription
for years and has some evidence of effectiveness, but its slow
absorption after ingestion makes it unappealing to some patients.

Several companies are working to make a dronabinol mist that could be
taken in a standardized dose with an inhaler, such as is done with
medicines for asthma. An alternative approach, being tested at UCSF,
is to heat marijuana in a vaporizer so that THC can be inhaled
without the carcinogens found in marijuana cigarettes.

If these technological breakthroughs are achieved, some physicians
will become more comfortable with prescribing THC. But others will
have the opposite reaction because purified, inhalable (and therefore
fast-acting) THC could carry more addictive risk than marijuana itself.

Addiction medicine specialists are aware of this possibility, which
may be why the Brown University survey showed that they were less
sanguine about medical marijuana than doctors in any other specialty.

In general, as plant-based compounds that can produce dependence are
processed and purified (e.g., from coca leaf to cocaine or opium
poppy to morphine) or are administered through a more rapid,
efficient route (e.g., from ingesting to smoking), their power to
produce addiction increases.

In other words, the very dosing technology that could makes THC more
pure and potent as a medicine may also make it more likely to produce
dangerous dependence. Unless further research reveals a way to cut
that Gordian knot, THC will probably remain a bit player in
mainstream medicine practice.