Marijuana Myths – Adverse Effects Of Cannabis

November 12, 2019

Anti-pot propagandists have ascribed many other adverse effects to marijuana. Indeed, many of these claims about marijuana’s toxicity never seem to die. A considerable amount of these arguments were widely publicized in the 1980s by the government and anti-pot groups, but have since been disproved.




Fertility & reproduction

Fertility and reproduction when using cannabis

Experts at the National Institute on Drug Abuse now report that pot has no permanent effect on the male or female reproductive systems. There have been exactly zero cases of impaired fertility among marijuana users of both sexes. If anything, marijuana may cause mild, temporary disruptions in ovulation, fertility, and menstrual cycles. Studies have also failed to prove that marijuana lowers testosterone and other sex hormone in men or women.

Brain damage

Cannabis brain damage

Even NIDA experts have admitted that pot doesn’t kill brain cells. This myth was largely based on some highly suspect animal experiment conducted by Dr. R.G. Heath, in which monkeys were exposed to uncertain levels of smoke. It was rather soundly disproven by calculated research conducted at the National Center for Toxicological Research and SRI International (Morgan). Human studies in Jamaica and Costa Rica have shown little or no evidence to support the “brain damage” claim.

Heavy marijuana use does cause calculably lower performance in some cognitive tasks like memory, concentration, verbal fluency, learning ability, and recall. These effects can last for days, but are almost always short-term. Indeed, research by Dr. Harrison Pope at McLean Hospital in Belmont, Massachusetts found that cognitive impairment among heavy users lasted between 1 to 7 days and never after 28 days. Dr. Pope suggested that mental impairment from marijuana is reversible (Pope and Solowij). Dr. Igor Grant, a professor of psychiatry at the University of California-San Diego and director of California’s Center for Medicinal Cannabis Research, reaffirmed Dr. Pope’s conclusion in an analysis of 15 prior studies (Grant). Dr. Grant was surprised that chronic marijuana use did not cause permanent brain damage seeing as how heavy use of alcohol, amphetamines, and other drugs can.

Chromosome and cell damage

Cannabis chromosome and cell damage

Claims that THC causes chromosome and gene damage work off of outdated studies in the 1970s that have now been soundly disproved (Morgan & Zimmer).

Immune system

Cannabis and your immune system

Frequently, pot critics have argued that THC impairs the immune system. The apparent immunosuppressive effects of THC were first analyzed and reported in lab studies in the 1970s. These studies found that THC mildly inhibited the activity of certain immune cells (particularly T-cells). In large part, these effects are mild and subtle. Zero cases of human immune system deficiency caused by THC have been observed epidemiologically or in clinical studies. As we’ve seen, studies of HIV/AIDS patients have provided no evidence of harmful immunosuppressive effects from marijuana. In fact, there’s evidence that THC can actually stimulate immune cells and improve T-cell counts.

But, immune suppression can be concerning in certain situations and, specifically, those in which the body’s immune response is needed to prevent infections caused by hostile organisms. In reality, cannabinoids do not so much suppress the immune system as modulate it, increasing certain responses and dampening others. Professor Robert Melamede of the University of Colorado Biology Department says that the immune system is balanced between two distinct pathways called Th1 and Th2. The Th1 response usually promotes inflammation to ward off infections while the Th2 response is naturally anti-inflammatory. Cannabinoids generally suppress the Th1 response and promote the Th2 response. The Th1 response is vital for fighting off infectious organisms like those that cause tuberculosis and Legionnaire’s disease. In that way, it’s probably a good idea to avoid marijuana if you need the Th1 response. If you don’t require a healthy immune response, there are other diseases like arthritis, rheumatism, diabetes, and Crohn’s disease that require the anti-inflammatory properties of the Th2 response.

Some people might be especially vulnerable to adverse immune effects. We’re familiar with one patient who had genital warts (papilloma virus infection) and resisted treatment whenever he used marijuana. Different lab studies have shown that marijuana may actually promote herpes infections in animals. Conversely, some patients insist that marijuana relieves herpes. It’s always best for patients to be aware of any reactions, both adverse and beneficial.

In contrast to oral THC, smoked marijuana actually impairs the immune response of the lungs. This isn’t related to the cannabinoids but, instead, the pyrolytic (combustion-produced) toxins in the smoke that attack the lung’s immune cells, its hair-like cilia, and other defense mechanisms. You can avoid these hazards by ingesting and vaporizing marijuana.

Gateway to hard drug addiction

Cannabis a gateway to hard drug addiction

Perhaps the most popular myth bandied about by anti-pot propagandists is that marijuana is a “gateway” to harder drug abuse (i.e. it leads to heroin, cocaine, and other addictive drugs). There is no pharmacological basis for this idea, because THC will never program the brain to crave harder drugs. The myth comes from a superficial observation that marijuana is often the first in a string of illegal drugs for many people. Of course, alcohol, tobacco, caffeine, and even mother’s milk all tend to predate marijuana use. The only significant difference is that marijuana isn’t legal and people must obtain it from criminal dealers who frequently traffic other illegal drugs. In this way, marijuana is not a gateway to addiction but to the illicit drug market.

Scientific researchers have repeatedly rejected this gateway theory. The La Guardia Report was among the first scientific studies to legitimately examine the issue (NY Academy of Medicine). It concluded: “The practice of smoking marijuana does not lead to addiction in the medical sense of the word,” and “the use of marijuana does not lead to morphine or heroin or cocain addiction…” A recent University of Pittsburgh study of adolescent boys found that marijuana use is not a reliable indicator of later substance abuse (Tarter).

The notorious head chief of the Federal Bureau of Narcotics, Harry Anslinger, popularized the gateway theory. Ironically, Anslinger had initially denied the theory in his testimony to Congress about the 1937 Marihuaba Tax Act. When asked about the connection between marijuana use and addiction to opium or cocaine, Anslinger replied, “No sir: I have not heard of a case of that kind. I think it is an entirely different class. The marijuana addict does not go in that direction,” (King). Of course, later when Anslinger testified in favor of the Narcotic Control Act of 1956 which included tougher penalties for marijuana, he said, “That is the great problem and our great concern about the use of marijuana, that eventually, if used over a long period, it does lead to heroin addiction,” (King).

The real fallacy behind the gateway theory is that cannabis-tolerant societies in India, Jamaica, and the Netherlands have no higher rates of heroin or other hard drug abuse than any other country.


Cannabis and violence

Contrary to myth, marijuana does not promote violent behavior. In fact, it tends to suppress it. The idea of reefer-crazed madmen driven to mayhem surfaced through scare stories in the 1920s. These were, of course, exposed as fabrications and later scientific studies showed that marijuana tended to promote passivity more than anything else. This was the finding of New York’s LaGuardia Report, which came to the conclusion that, “there was no aggressiveness or violent behavior observed.”

“Marihuana and Health,” a National Academy of Sciences report, stated, “Both retrospective and experimental studies in human beings have failed to yield evidence that marijuana use leads to increased aggression. Most of these studies suggest quite the contrary effect. Marijuana appears to have a sedative effect, and it may reduce somewhat the intensity of angry feelings and probability of interpersonal aggressive behavior.”

It seems the laidback hippie, not the murderous bandit, turn out to be the more realistic stereotype of a pot smoker after all.

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The founder of I Love Growing Marijuana, Robert Bergman, is a marijuana growing expert that enjoys sharing his knowledge with the world. He combines years of experience, ranging from small-scale grows to massive operations, with a passion for growing. His articles include tutorials on growing... [read more]


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  1. By joey ,15 Mar 2013
    Too bad you don't have details on the protective effects of the CB1 and CB2 receptors and the roll of the cannibadiols in healing and regulating. And you seem to entirely miss the roll of raw juiced cannabis, which is […]Read More
  2. By Adverse Effects Of Marijuana, Real and Imaginary – ,05 Apr 2016
    […] publicized in the 1980s by the government and anti-pot groups, but have since been disproved. Common myths […]
  3. By sean ,31 Jan 2017
    Forty years and I haven't seen any such adverse effects at all! Only good effects. Use to drink, no more. This god given plant is one of a ton of natural cures, but one of the best. For me sleep, […]Read More
  4. By Dawn ,31 Jan 2018
    I’m “New” and I’m looking for a strain that doesn’t increase my appetite and more importantly doesn’t make me dizzy. I’ve tried Blue Dream and Lemon Ice both caused severe dizziness. The dizziness lasted for about 18 hours and caused […]Read More
    1. By latewood_ILGM ,18 Apr 2018
      Dawn,\ Sorry for the late reply. You should look into CBD oil made from hemp. There is no ThS (makes you dizzy) All the astrains you mention have a pretty high THC level and you should be looking for high […]Read More
  5. By Noreen Renier ,29 May 2018
    I am having a strong reaction to medical marijuana, it weakens my muscles in my upper arms, I can't lift my arms from the shoulder to the elbow. Is the CBD or the THC causing this?
    1. By latewood_ILGM ,01 Jun 2018
      Noreen, This is not something that can be judged after a simple question or comment in a blog. I suggest you join us at: and you will be opened up to many helpful friendly sharing medical marijuana patients that […]Read More

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