TRUE EFFECTS OF MARIJUANA ARE STILL UNKNOWN

Marijuana shook off its "weed-with-roots-in-hell" reputation decades ago,
after scientific studies punctured old myths and challenged popular
misconceptions about the drug.

Folklore about marijuana dates to a classic 1936 film, Reefer Madness:
Devil 's Harvest. It showed marijuana causing instant addiction, a craving
for heroin, crime sprees, and insanity.

Newer studies gradually painted a different portrait of marijuana as a drug
that rarely leads to addiction or serious crime by users. Marijuana found a
niche in medicine. Although rarely used, it is a second-line drug that can
relieve nausea and vomiting and certain other problems when other drugs fail.

Millions of Americans have tried marijuana. A 1999 National Academy of
Sciences (NAS) report estimated that one-third of the U.S. population over
age 12 - 69 million people - had tried marijuana at least once. Most used
marijuana for brief periods in their teens or 20s, and stopped.

The growing acceptance of marijuana has fostered a new misconception,
especially among younger people: That all the scientific uncertainties
about marijuana's safety have been resolved. Marijuana, they believe, is a
totally harmless substance persecuted by overly zealous law enforcement
officials.

In reality, serious scientific questions about marijuana's effects and
safety remain unanswered.

They extend beyond possible health problems from inhaling marijuana smoke
into the lungs. As NAS noted, marijuana smoke, like tobacco smoke, contains
carcinogens and other harmful chemicals.

Inhale smoke containing those substances, and the toxic materials go into
the blood and circulate throughout the body.

One of the most serious unanswered questions involves marijuana's effects
on brain cells.

Here's the situation:

Marijuana interferes with the normal workings of brain cells.

That's why marijuana produces its "high" and causes changes in the way a
user thinks and senses the world.

Computerized brain images of heavy marijuana users show different patterns
of blood flow and nerve cell activity.

Psychological tests of long-term users also show unusual problems with
"cognitive functioning." That means problems with memory, focusing
attention, performing complex tasks, and other problems.

A scientific debate is under way - largely hidden from public view - on the
importance of those changes. Do brain cells fully recover after a person
stops using marijuana, with the memory impairments disappearing? Or does
marijuana have a toxic effect on nerve cells that slowly causes lasting
damage that worsens after years of use?

Studies in animals reinforce the concerns. They show that marijuana's
active ingredient alters the activity of a brain system critical for normal
memory.

Experts agree that cognitive changes last for hours or days after a person
uses marijuana. But they disagree on whether those problems last longer and
grow worse over time.

The disagreements are sharp, and one study may reach conclusions exactly
the opposite of another.

Early in March, for example, an international research group reported that
cognitive impairments do last and worsen. They studied 102 people who had
used marijuana almost daily for years.

"The kind of impairments observed in this study have the potential to
impact academic achievements, occupational proficiency, interpersonal
relationships, and daily functioning," they reported in the Journal of the
American Medical Association (JAMA).

Mental impairments, researchers said, develop silently and may be apparent
only after 10 or 20 years of heavy marijuana use.

A year earlier, equally distinguished researchers found no lasting ill
effects after studying 108 heavy marijuana users.

"We still must live with uncertainty," Harvard University's Dr. Robert G.
Pope, Jr., summed up the situation in a JAMA editorial.

Today's marijuana users will do the same - with their own long-term health
at stake - as unknowing subjects in a huge, real-life experiment. Their
fate will help scientists paint marijuana's final portrait.