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Top 11 Marijuana Myths Debunked

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Some marijuana myths exaggerate its dangers, and others play them down. The National Cancer Institute says lethal overdoses from cannabis do not occur, but that does not make it harmless: it can affect memory, the developing brain and a pregnancy. Here is what federal health agencies and published studies say about 11 common myths.

Some myths go back to Reefer Madness, a 1930s propaganda film that told viewers marijuana would turn them into deranged criminals who jump out of apartment windows.

Times have changed, and research has since filled in the picture: most people who use cannabis do not move on to other drugs, according to NIDA, but cannabis can be addictive, affects memory, learning and attention and should be avoided in pregnancy.

But marijuana myths are still out there, circulating the web. And with the rise of “fake news” sites, it’s hard to know what’s true and what’s not.

Our job is to educate people so that they use medical marijuana safely and responsibly.  We want to help you separate fact from fiction.

Each myth below is checked against NIH, CDC, FDA or MedlinePlus pages or a study in PubMed.

1).  “Marijuana Is Harmless to the Brain”

If you were a child of the 1980s, you might remember the “This Is Your Brain on Drugs” commercials. They compared your brain to an egg and drugs to a frying pan, with the message that drugs fry your brain.

The commercial ends famously with the line, “Any questions?”

Here’s a question:  why does the commercial use “drugs” as a blanket term without drawing a distinction between something like marijuana and something like cocaine?

Cocaine, by the way, can absolutely damage your brain.  Don’t do it.

But marijuana is not harmless to the brain either: studies suggest that marijuana can negatively affect the developing brains of adolescents.  In adults, whether cannabis causes lasting brain damage is less clear, though CDC notes that cannabis directly affects the parts of the brain used for memory, learning and attention.

CBD-based medicine has been tested in children mainly for certain seizure disorders, so its long-term effects on the developing brain are not well known.  Finally, some lab and animal studies suggest cannabinoids may protect brain cells, but a 2021 Cochrane review of dementia trials could not confirm a benefit.

2).  “Marijuana Has No Effect on Memory”

THC can affect your short-term memory while you’re under its influence.  However, a 2001 study of 180 adults found that word-recall problems in heavy users had largely faded after 28 days without cannabis. NIDA notes that regular, heavy use in adolescence is linked to longer-term effects, and CDC says that when use starts before age 18, effects on attention, memory and learning may last a long time or even be permanent, though more research is needed.

3).  “You Can Die From a Marijuana Overdose”

This is one of those marijuana myths that has been so thoroughly debunked that we wondered if it was even worth mentioning.

The National Cancer Institute explains that cannabis does not act on the brainstem areas that control breathing, which is why fatal overdoses are not known to occur. Our post on whether you can overdose on marijuana covers this question in more detail.

Sure, people have done irresponsible things while under the influence of marijuana, and they may have died as an indirect result.

That does not make large amounts harmless: NIDA reports medical emergencies from cannabis edibles, including in children.

Too much THC can still cause anxiety, confusion and vomiting; FDA has received such reports for delta-8 THC products.

4).  “Marijuana is a ‘Gateway Drug'”

The gateway idea is more complicated than it sounds, and it still finds its way into the media and political discourse.

For most people, marijuana is not a gateway drug. Our post on whether marijuana is a gateway drug goes deeper, with NIDA and CDC sources.  According to NIDA, cannabis is among the first substances people encounter, along with alcohol and tobacco, and most people who use it do not go on to use other substances.  Still, NIDA notes that cannabis use may cause brain changes that make addiction to other drugs more likely.

Some people argue that the gateway effect is a social and legal issue rather than a pharmacological one, but NIDA’s summary of the research also describes possible brain changes, so the question is not settled.  Because marijuana is still federally controlled and illegal in certain states, many people buy it on the black market.  That means they buy from illegal sellers, who may sell other drugs too.

Under Florida law, licensed treatment centers are the sole legal source of marijuana for qualified patients.

Some argue that the black market, not marijuana, is the real gateway.

5).  “THC Has No Medicinal Value”

A lot of attention has gone to CBD because it does not cause a high.  THC, on the other hand, is considered to be the cannabinoid that “gets you high,” so you don’t really need it.

This couldn’t be further from the truth.  THC does have medical uses: dronabinol, a lab-made THC, is FDA-approved for chemotherapy nausea and for appetite loss in AIDS, and NIH notes modest evidence for some chronic pain.

Some people believe that if you just pull the active ingredients out of marijuana, you don’t need the entire plant.  But it’s not that simple.  Cannabis also contains terpenoids and flavonoids, and some researchers think they work together with cannabinoids, an idea called the “entourage effect” that clinical trials have not proven.

6).  “You’ll Increase Your High If You Hold the Smoke In Your Lungs For a Long Time”

If you have heard this one, here is what a small study found.

A 1989 study of 8 regular smokers found that holding marijuana smoke for 10 or 20 seconds did not clearly strengthen its effects compared with exhaling at once.  Holding it in does keep the smoke in your lungs longer, and NIDA notes that cannabis smoke contains many of the same toxins, irritants and carcinogens as tobacco smoke.  The longer hold buys more exposure, not a clearly stronger effect.

7).  “Blunts Are Just Bigger Joints”

Blunts are wrapped in tobacco. A 2023 study describes blunt smoking as using a tobacco-derived cigar shell or wrap, which exposes people to non-trivial amounts of nicotine. The same study found that people who smoked blunts were more likely to start smoking cigarettes and cigars.

Joints, on the other hand, are made out of plain old paper.  There’s nothing intoxicating about them.

A blunt can also hold more marijuana than a joint, and more marijuana means more THC.

Blunts might save you rolling papers, but they do not make marijuana stronger; any extra THC comes from the extra marijuana inside.

8).  “Water Pipes Make Marijuana Smoke Safe”

“But what about bongs?” you might be asking.  “Doesn’t the water make the smoke safe?”

No study we found in PubMed shows that it does, and whether bongs get you higher than joints is not settled either.

A smoother or cooler hit from a water pipe is not evidence that the smoke is any cleaner.

Water does not make smoke safe: CDC notes that cannabis smoke carries many of the same toxins and carcinogens as tobacco smoke.

9).  “Marijuana Has No Effect on Sperm”

If you are a man who uses medical marijuana and want to have children, here is what one large study found.

A 2015 study of 1,215 young Danish men found that smoking marijuana more than once a week was linked with 28% lower sperm concentration. Whether the effect lasts after stopping is not well studied.

If you’re trying to have kids, ask your doctor about putting away pipes, joints, vaporizers and edibles while you try.

One study cannot settle the question, but the Danish result is worth raising with a physician if you are trying to conceive.

10).  “Marijuana Is Safe During Pregnancy”

Before we tackle this controversial marijuana myth, we need to say that we at Dr. Green Relief do not advocate or endorse the consumption of marijuana during a pregnancy.  If you’re a pregnant mother who’s considering using marijuana either before, during, or after a pregnancy, you need to consult with your physician and be fully aware of the potential risks.

With that said, the evidence starts with one small, older study.

A small study in rural Jamaica, published in 1994, compared 24 newborns exposed to marijuana before birth with 20 who were not and found no harm in the first month, but it measured newborn behavior only.

The exposed babies scored better at one month, and the researchers themselves suggested that this was traceable to the mothers’ cultural, social and economic circumstances rather than to marijuana.

Larger studies since then point the other way: CDC says cannabis use in pregnancy can lower birth weight and affect brain development, and advises pregnant women to avoid it.

11).  “Marijuana Stays In Your System for 30 Days”

How long THC stays detectable depends on how much you use, how long you have used it and how your body reacts, according to MedlinePlus.

THC is stored in your body’s fat cells, so if you’re constantly smoking marijuana, THC can build up in your system and linger there.  Drug tests can find signs of drugs taken hours to several days or more before the test, so even occasional use can show up.

Do you know of any marijuana myths that weren’t covered in this post?  If you do, give us a shout-out on our Facebook page.  And feel free to contact us directly if you have any questions about marijuana myths or facts.

Last updated October 17, 2026 by the Dr. Green Relief Editorial Team.

Medical review

Medically reviewed by Achilles Kalnoky, M.D.

Reviewed on .

He is licensed in Florida as a medical doctor, license ME115088, which you can check on the Florida Department of Health license lookup.

His review covers the medical statements in this post and the sources cited for them.

Sources

About the Author

Dr. Green Relief Editorial Team

The Dr. Green Relief editorial team writes and updates the articles on this blog. They are general information, not medical advice; talk with a licensed physician about your own care. Medical review, where shown, applies only to the Florida pages that carry a review date.

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