Although research into the health effects of marijuana often produced contradictory results, relatively disinterested assessments concluded the smoke irritates the throat and lungs and has as many carcinogenic compounds as tobacco.
PHOTO: FOTOLIA/RICHARD VILLALON
Dr. Tom Ferguson wrote the Medical Self Care column in this magazine in the early 1980s. This issue's column was guest authored by Michael
Castleman, managing editor of Medical Self-Care magazine.
Two years ago, investigators at the UCLA Pulmonary Research
Laboratory published the abstract of a study on the
respiratory effects of heavy marijuana smoking among 75
young men who consumed an average of five marijuana
cigarettes, or joints, a day for two months. Among other
less dramatic findings, this "Tashkin Report" suggested:
"Smoking four joints a week may cause more respiratory
impairment than smoking 16 cigarettes a day."
The wire service that picked up the story dropped the word
"may," and the nation learned that the lung damage
caused by four joints equaled that caused by 112
Later that year, Peter Bensinger (a director of the federal
Drug Enforcement Agency) told a graduating class at the FBI
Academy that smoking five joints a week introduced more
carcinogens into the lungs than smoking a pack of
unfiltered cigarettes a day. His remarks were also picked
up by the wire services.
Extrapolations like these occur with disturbing frequency.
Because marijuana is controversial—and
illegal—the atmosphere surrounding the health effects
of marijuana is highly charged, and the available data conflict at
almost every turn. In fact, if all marijuana researchers
are correct in their methodological criticisms of each
other's work, none of the reported results can be trusted.
On the other hand, no reputable authorities argue that
"grass" is completely safe, not even the legalization
lobby, the National Organization for the Reform of
Marijuana Laws (NORML). Clearly, lung cells are extremely
delicate, and any long-term exposure to hot particulate
combustion products—which contain a large number of
carcinogens—can be assumed to cause some damage.
The question is, how much harm is caused by how much
smoking? The research, contradictory as it is, falls into
two general categories indicating either that pot is
"not all that harmful" or that it's "very harmful".
"Not All That Harmful"
The best collection of papers indicating that marijuana is
relatively benign—even when used to excess—is
"Chronic Cannabis Use," published by the New York Academy
of Sciences. The report chronicles studies in Costa Rica
and Jamaica dealing with a wide range of health variables
in heavy marijuana smokers as compared to non-pot-smoking controls. "Heavy" use in
Jamaica would be considered nonstop smoking by United
States standards, since the average user tested had
consumed seven high-potency joints a day for 17.5 years.
The studies compared smokers' and nonsmokers' physical
exams, electrocardiograms, blood, immunity to infection,
testosterone levels, chest X-rays, lung function, and
chromosome integrity .. and showed "no significant
differences between the two groups in the wide range of
The leading researcher with a negative perspective is
Gabriel Nahas—an anesthesiologist at Columbia
University in New York—who summarized the case
against marijuana last year in the Journal of the American
Medical Association. He reported that cannabis use
interfered with cell division; harmed lung tissue
significantly, with the damage persisting long after
cessation of smoking; lowered the lungs' defenses
against bacteria "substantially more" than does tobacco; reduced sperm counts and decreased testosterone levels
(although these effects were reversible after the users
stopped smoking marijuana); caused birth defects;
hindered brain function; impaired judgment while
driving; and perhaps (this point was not considered
proven) triggered epileptic seizures.
Two Official Perspectives
Two organizations have attempted to make sense of the
conflicting data: NIDA (a division of the U.S. Department
of Health and Human Services) and its Canadian counterpart,
the Addiction Research Foundation (a branch of the Ontario
Ministry of Health). Neither of the organizations can be
considered a completely disinterested observer, since
their funding comes from legislative bodies which have kept
marijuana illegal. But despite possible bias, the reports
are fairly consistent with each other and provide
reasonable overviews of the current "official" consensus on
the adverse effects of this drug. Here are the agencies'
 Smoking pot irritates the throat and lungs and may
cause bronchitis in heavy users.
 Careful comparison of smoke condensates shows that one
joint deposits about 50% more "tar" in the lungs than does
one nonfiltered cigarette, largely because joints tend to
be smoked down to smaller butts, and pot smokers typically
hold the smoke in their lungs longer.
 Marijuana's smoke has as many carcinogenic polycylic
aromatic hydrocarbons (PAH's) as tobacco smoke does,
although some PAH's—benzopyrene, for
example—are more abundant in pot smoke, while others
are less. Marijuana, however, contains neither
nicotine—which is a very potent poison—nor (in
most cases) the pesticide residues typically found in
tobacco smoke, which may accelerate the tumor-inducing
effects of PAH's.
 The use of marijuana increases the heart rate and may
prove hazardous to those with heart diseases. It also
reduces testosterone levels in men to the lower end of the
normal scale, though these levels do rise again after
the cessation of smoking. The drug also appears to reduce
both sperm count and sperm motility. The active ingredient
in marijuana, delta-9-tetrahydrocannabinol (THC),
apparently stimulates these changes, because it binds to
estrogen (the female hormone) receptors and exerts "a weak,
but significant" estrogenic effect. (This activity may be
the reason why there've been anecdotal reports of breast
development, gynecomastia, in men who were heavy users.)
 THC crosses the placenta and has been found in the milk
of lactating laboratory animals, and large doses of THC
have been shown to increase the fetal death rate in rhesus
 Marijuana may suppress certain immune responses in the
lungs, making users more susceptible to infection, but the
research is inconclusive, and this question hasn't been
fully investigated in humans.
 Users freely admit that the drug causes disorientation,
and school officials have expressed concern about what they
refer to as the "antimotivational syndrome" associated with
 Marijuana impairs driving performance, and—when
pot is used with alcohol—the user's ability to
operate a vehicle deteriorates even further.