Marijuana use and schizophrenia: New evidence suggests link

A new study, published in Psychological Medicine, has added to the body of evidence pointing to a link between schizophrenia and the use of cannabis.

New research finds that people with schizophrenia are more likely to smoke cannabis.

Recent research suggests that not only are people who are prone to schizophrenia more likely to try cannabis, but that cannabis may also increase the risk of developing symptoms.
Studies show that cannabis use is more common among people with psychosis than in the general population, and that it may also increase the risk of psychotic symptoms.
Its use has been linked to symptoms of psychosis, such as paranoia and delusional thinking, in up to 40 percent of users.
Earlier this year, scientists warned that young people who use cannabis could be putting themselves at risk of psychotic disorders. People with schizophrenia appear to have a higher chance of experiencing psychosis if they use cannabis.
Previous warnings had voiced concerns regarding the particularly powerful strains of cannabis, such as "skunk," currently circulating among young people.
However, the findings were not considered definite and experts called for more research.

Genome data reveals possible link

Now, Dr. Suzi Gage and team, from the School of Experimental Psychology at Bristol University in the United Kingdom, have discovered more evidence that cannabis may be particularly hazardous to people with schizophrenia, although they highlight that other factors also impact mental health.

Fast facts about cannabis

• Around 44 percent of 12th graders have used marijuana in their lifetime
• An estimated 46 percent of people in the United States aged 26 and over have used it
• Approximately 12.8 percent of 8th graders have used the drug, with 0.7 percent using it daily.

Learn more about marijuana

The authors looked at genetic factors that may predict whether a person is likely to use cannabis, and whether they are likely to develop schizophrenia. The data was taken from a wide-ranging genome study.
The Mendelian Randomization technique, used to analyze the data, enabled the authors to account for a range of variants.
This technique was chosen because the team predicted that people who use cannabis are likely to be genetically and biologically different from those who do not in a variety of ways.
Findings indicate that starting to use cannabis may increase the risk of schizophrenia, but especially that a person who is at risk of schizophrenia is more likely to use cannabis.
This may be because genetic factors for schizophrenia are stronger than those for cannabis use.
The study authors would like to investigate whether a genetic link might explain the extent of cannabis use, because results show that people with schizophrenia are more likely to be heavy users of cannabis.
Medical News Today asked the authors why people with a risk of schizophrenia might be more likely to use the drug.
Prof. Marcus Munafò, a member of the team, speculated that "certain behaviors or symptoms associated with schizophrenia risk might be relieved by the effects of cannabis." In other words, cannabis use may be a kind of self-medication in this population.
An alternative explanation, he said, is that "people with higher risk of schizophrenia may enjoy the psychological effects of cannabis more."

"There is growing consensus that cannabis use might increase the risk of developing schizophrenia. Our results support this, but also suggest that those at increased risk of schizophrenia may be more likely to try cannabis in the first place."

Prof. Marcu Munafò

MNT asked the researchers what role cannabis might play in raising or lowering the risk of schizophrenia.
Prof. Munafò pointed out that while further studies are needed, existing research suggests that two of the constituents of cannabis, tetrahydrocannabinol (THC) and cannabidiol (CBD), might have an impact.

The roles of CBD and THC

THC intoxication has been associated with transient psychotic experiences. CBD, on the other hand, does not trigger mind-altering experiences and may have potential as a medication, according to the National Institute on Drug Abuse (NIDA).
NIDA point out that most recreational marijuana is high in THC and low in CBD.
Dr. Gage and colleagues predict that the proportion of THC to CBD will probably be significant in psychotic symptoms. 

In addition, Prof. Munafò told MNT that results will be needed from multiple sources, including laboratory and epidemiological studies, before any definite conclusions can be reached.
Limitations of the study include the relatively small overlap between cannabis users and people with schizophrenia in around 1,500 people.
Until now, there have been too few consistent studies to compare the effects of cannabis, and as a result, assessing the impact of cannabis on brain structures has remained a challenge. However, it has been found that people with schizophrenia who use cannabis are more likely to be hospitalized than those with the condition who do not use the drug.
Dr. Gage expresses an interest in looking more closely at the subgroups of more vulnerable cannabis users, in order to gain a better understanding of how heavy usage might influence their well-being. 

Most marijuana users enjoy the drug’s ability to induce a sense of euphoria, but that doesn’t come without side effects.

Indeed, research shows that using marijuana can cause a variety of short and long-term effects.
While almost everyone is familiar with the sudden desire for junk food caused by smoking weed — commonly referred to as the ‘munchies’ — many of the drug’s other effects are lesser known.
Here are 9 of the most common side effects of using cannabis:

1. Dry Mouth

(Photo: NIH/Wikimedia Commons)

Most people who use marijuana are familiar with the side effect referred to as ‘cottonmouth’, meaning that users experience an uncomfortable feeling from lack of saliva production.
A survey published in the journal of Addiction Research & Theory in 2003 found that 79% of marijuana users experience dry mouth.
“In a lot of cases, you would expect to see more of the dry mouth in a recreational user because they’re consuming, generally speaking, a lot more cannabis than the average medical user,” says Johnathan Werynski, Senior Cannabis Counselor at CanvasRX, a company that provides assistance to Canadians who have been prescribed cannabis by their doctors.
Users can help minimize the effect by chewing on gum or food, which can stimulate the salivary glands to produce saliva.

2. Dizziness

(Photo: Pixabay)

Many users report feeling dizzy after smoking cannabis, particularly when they stand up.
In a 1992 study, 60% of participants reported moderate to severe dizziness while standing after smoking a high-potency marijuana joint.
The individuals in the study who experienced severe dizziness also showed decreases in blood pressure, which provides a plausible explanation for this effect.
However, studies also show that frequent users can develop a tolerance to many of marijuana’s short-term effects, including feelings of dizziness.

3. Increased Appetite

(Photo: Love From The Oven/Flickr)

One of the most known side effects of marijuana is the ‘munchies’. Shortly after smoking, many users will experience a sudden increase in appetite, often leading them to raid their fridge.
Though scientists are still unsure of the exact mechanism behind this effect, a 2015 study suggested that marijuana might activate certain pathways in the brain related to hunger.
While some view this side effect as negative, it’s a benefit to people who use marijuana to treat appetite loss during chemotherapy.
In fact, a pill containing THC (Marinol) is available in a number of countries for patients with cancer.

4. Memory Impairment

(Photo: Hey Paul Studios/Flickr)

Many studies have found that cannabis users experience short-term memory problems; other studies suggest that cannabinoids impair all stages of memory.
Young people who use the drug may be most at risk. A 2011 study suggested that memory impairment is more severe in adolescent cannabis users, and might even have a lasting impact.
However, frequent users often become tolerant to the memory problems cannabis can cause.

5. Lack of Motivation

(Photo: Pixabay)

Some people who are against the use of recreational marijuana point to the stereotype that users become unmotivated at work and in school. While this cliché is exaggerated, there is some merit to the belief.
In a 2003 survey, 53% of marijuana users reported experiencing a loss of motivation.
The loss of motivation might be explained by how cannabis affects the brain. Some studies suggest that long-term cannabis users have lower levels of dopamine — a chemical in the brain that is directly responsible for motivation.

6. Depression

(Photo: JoePenna/Flickr)

Although it has been proven that cannabis can act as a medicine to help people combat depression, in some cases it might work the opposite way.
According to Werynski, research suggests that marijuana can cause depression mostly in young people. Likewise, a study published in 2002 in the British Medical Journal concluded that frequent cannabis use in teenage girls predicts depression in later years.
Still, it’s important to note that there are different types of depression and that marijuana may affect each type differently.

7. Paranoia/Anxiety

(Photo: Hunter McGinnis/Flickr)

Another mental side effect of marijuana is the paranoia users often experience after smoking.
“There absolutely is documented evidence in medical literature that THC can affect people by bringing on anxiety or elevating anxiety,” says Werynski.
A 2015 study found that THC increased paranoia in individuals who had previously experienced the symptom. But the study also revealed that paranoia wasn’t a direct result of THC. Instead, paranoia seemed to be a byproduct of other effects of cannabis (such as depression) and the feeling of having an unusual experience.
A study published in the late 80s found that patients with panic anxiety were likely to experience increased anxiety from marijuana. However, Werynski notes that CBD can actually act to reduce anxiety.

8. Addiction

(Photo: Presna 420/Flickr)

Like most drugs, there’s a risk of addiction associated with cannabis use.
When an individual stops using cannabis, cannabinoid receptors must adjust back to normal levels, which leads to psychological and physical withdrawal symptoms.
A 2010 study found that 42% of users who tried to quit experienced withdrawal symptoms, such as irritability, sleep difficulty, and decreased appetite.
Although some people do not believe cannabis to be addictive, researchers stand firm on their findings.
“Cannabis is a psychoactive drug which activates the same brain reward regions as do other abused drugs, such as alcohol, tobacco, cocaine, etc.,” explains Dr. David Gorelick, a professor of psychiatry at the University of Maryland School of Medicine.

9. Lung Problems

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Like cigarettes, smoking marijuana can have detrimental effects on a user’s respiratory system.
“Anything that lights the plant on fire creates respiratory irritants,” says Dr. Mitch Earleywine, a professor and researcher at the State University of New York at Albany.
Studies show that people who smoke marijuana can suffer from respiratory problems, such as bronchitis, coughing and wheezing.
“We don’t advise people to smoke cannabis at all anymore,” says Werynski, who instead recommends using a vaporizer.

What are marijuana's long-term effects on the brain?

Substantial evidence from animal research and a growing number of studies in humans indicate that marijuana exposure during development can cause long-term or possibly permanent adverse changes in the brain. Rats exposed to THC before birth, soon after birth, or during adolescence show notable problems with specific learning and memory tasks later in life.^31–33 Cognitive impairments in adult rats exposed to THC during adolescence are associated with structural and functional changes in the hippocampus.^34–36 Studies in rats also show that adolescent exposure to THC is associated with an altered reward system, increasing the likelihood that an animal will self-administer other drugs (e.g., heroin) when given an opportunity (see "Is marijuana a gateway drug?").
Imaging studies of marijuana’s impact on brain structure in humans have shown conflicting results. Some studies suggest regular marijuana use in adolescence is associated with altered connectivity and reduced volume of specific brain regions involved in a broad range of executive functions like memory, learning, and impulse control compared to non-users^37,38 Other studies have not found significant structural differences between the brains of users and non-users.³⁹
Several studies, including two large longitudinal studies, suggest that marijuana use can cause functional impairment in cognitive abilities but that the degree and/or duration of the impairment depends on the age when an individual began using, how much they used, and how long they used.⁴⁰
Among nearly 4,000 young adults in the Coronary Artery Risk Development in Young Adults (CARDIA) study tracked over a 25-year period until mid-adulthood, cumulative lifetime exposure to marijuana was associated with lower scores on a test of verbal memory, but did not affect other cognitive abilities like processing speed or executive function. The effect was sizeable and significant even after eliminating current marijuana users and after adjusting for confounding factors like demographic factors, other drug and alcohol use, and other psychiatric conditions like depression.⁴¹
A large longitudinal study in New Zealand found that persistent marijuana use disorder with frequent use starting in adolescence was associated with a loss of an average of 6 or up to 8 IQ points measured in mid-adulthood.⁴² Significantly, in that study, those who used marijuana heavily as teenagers and quit using as adults did not recover the lost IQ points. Users who only began using marijuana heavily in adulthood did not lose IQ points. These results suggest that marijuana has its strongest long-term impact on young users whose brains are still busy building new connections and maturing in other ways. The endocannabinoid system is known to play an important role in the proper formation of synapses (the connections between neurons) during early brain development, and a similar role has been proposed for the refinement of neural connections during adolescence. If long-term effects of marijuana use on cognitive functioning or IQ are upheld by future research, this may be one avenue by which marijuana use during adolescence produces its long-term effects.⁴³
However, recent results from two prospective longitudinal twin studies did not support a causal relationship between marijuana use and IQ loss. Marijuana users did show a significant decline in verbal ability (equivalent to 4 IQ points) and in general knowledge between the preteen years (ages 9 to 12, before use) and late adolescence/early adulthood (ages 17 to 20). However, at the start of the study, future marijuana users already had lower scores on these measures than future non-users, and no predictable difference was found between twins when one used marijuana and one did not. This suggests that observed IQ declines, at least across adolescence, may be caused by shared familial factors (e.g., genetics, family environment), not by marijuana use itself.⁴⁴ It should be noted, though, that these studies were shorter in duration than the New Zealand study and did not explore the impact of the dose of marijuana (i.e., heavy users) or the development of a cannabis use disorder; this may have masked a dose- or diagnosis-dependent effect. 
The ability to draw definitive conclusions about marijuana’s long-term impact on the human brain from past studies is often limited by the fact that study participants use multiple substances, and there is often limited data about the participants’ health or mental functioning prior to the study. Over the next decade, the National Institutes of Health is funding a major longitudinal study that will track a large sample of young Americans from late childhood (before first use of drugs) to early adulthood. The study will use neuroimaging and other advanced tools to clarify precisely how and to what extent marijuana and other substances, alone and in combination, affect adolescent brain development.

Marijuana, Memory, and the Hippocampus

Distribution of cannabinoid receptors in the rat brain. Brain image reveals high levels (shown in orange and yellow) of cannabinoid receptors in many areas, including the cortex, hippocampus, cerebellum, and nucleus accumbens (ventral striatum).

Memory impairment from marijuana use occurs because THC alters how information is processed in the hippocampus, a brain area responsible for memory formation.
Most of the evidence supporting this assertion comes from animal studies. For example, rats exposed to THC in utero, soon after birth, or during adolescence, show notable problems with specific learning/memory tasks later in life. Moreover, cognitive impairment in adult rats is associated with structural and functional changes in the hippocampus from THC exposure during adolescence.

As people age, they lose neurons in the hippocampus, which decreases their ability to learn new information. Chronic THC exposure may hasten age-related loss of hippocampal neurons. In one study, rats exposed to THC every day for 8 months (approximately 30 percent of their life-span) showed a level of nerve cell loss (at 11 to 12 months of age) that equaled that of unexposed animals twice their age.

Marijuana use is associated with an almost doubled risk of developing stress cardiomyopathy, a sudden life-threatening weakening of the heart muscle, according to a new study. Cannabis fans may find the results surprising, since two-thirds believe the drug has no lasting health effects. But as more states approve recreational use, scientists say there’s a renewed urgency to learn about the drug’s effects.
An estimated 22 million Americans — including 38 percent of college students — say they regularly use marijuana. Previous research has raised cardiovascular concerns: The drug has been linked to an increased risk of heart attack immediately after use, and a 2016 study in rodents found that one minute of exposure to marijuana smoke impairs the heart’s inner lining for 90 minutes, longer than tobacco’s effect.
The new study, presented November 13 during the American Heart Association’s Scientific Sessions, examined the occurrence of stress cardiomyopathy, which temporarily damages the tip of the heart.  Researchers from St. Luke’s University Health Network in Bethlehem, Pa., searched a nationwide hospital database and found more than 33,000 admissions for stress cardiomyopathy from 2003 to 2011. Of those, 210 were identified as marijuana users, and had about twice the odds of developing the condition, said Amitoj Singh, who led the study. Young men were at highest risk and more likely to go into cardiac arrest despite having fewer cardiovascular risk factors. Notably, the number of marijuana-linked cardiomyopathies increased every year, from 17 in 2007 to 76 in 2011. “With recent legalization, I think that’s going to go up,” Singh said.

Marijuana is widely used, especially in adolescents and young adults. In the US, there are about 20 million users (about 7.5% of people aged 12 or older).
Marijuana is a mind-altering (psychoactive) drug. Similar to hemp, it comes from the cannabis plant. The plant’s primary drug effects come from the chemical delta-9-tetrahydrocannabinol, or “THC.” Marijuana is smoked, “vaped” (inhaling the vapor), or ingested in foods or teas. Over the last few decades, the concentration of THC in the cannabis plant has been increasing. In addition, the plant extracts are more potent.

Short-term effects of marijuana

Marijuana is often used for its “high,” and can make people feel more relaxed, alter the senses, and cause time distortion. It can also impair thinking, judgment, coordination, and memory. In some people, it may lead to paranoia or anxiety. Physical effects may include bloodshot eyes, dry mouth, slurred speech, and increased heart rate.
These sensations may last up to four hours after inhaling marijuana smoke, or up to 12 hours if consumed, though performance impairments may last for much longer.

Long-term effects of marijuana

Smoking marijuana can irritate the lungs and lead to breathing problems like cough, excess mucus, bronchitis, and worsening of conditions like asthma and cystic fibrosis. It is not clear if smoking marijuana is linked to lung cancer. Marijuana use during pregnancy can also harm a baby’s brain development.
We are learning more about the long-term effects of marijuana, and this leads to even more questions as we realize there is a lot we don’t know. What is clear is that some of the long-term effects correspond to heavy use. However, heavy use is difficult to define given the nature and limitations of past studies, the different ways marijuana and its extracts are used, and the shifts in THC concentration in cannabis.
The biggest health risks appear to be in those who start using as teenagers or young adults when their brains are still developing. In youths who use heavily, studies have shown deterioration in their learning and cognitive thinking that persists into adulthood, even after they have stopped using marijuana. There also appears to be a link between marijuana use and certain mental illnesses. Though most marijuana users will not develop dependence and addiction, it is more common in teenage users.

Medical benefits of marijuana

Medical use of marijuana (“medical marijuana”) is somewhat controversial. In the United States, current FDA-approved medications containing synthetic THC are dronabinol (Marinol capsules, Syndros liquid) and nabilone (Cesamet). These drugs are prescribed as appetite stimulants in AIDS patients and for chemotherapy-related nausea and vomiting. They are sometimes used off-label for similar symptoms in other conditions. An oral spray nabiximols (Sativex) is approved in other countries for treatment of multiple sclerosis muscle spasticity and cancer-related pain not managed by other pain medication, and is undergoing further evaluation in the U.S.
Although marijuana can help relieve the symptoms of certain medical conditions, its use is still illegal on a federal level, and because we don’t have data from large, long-term, well-designed studies, the FDA continues to have concerns about potential risks versus benefits. Fortunately, studies continue on marijuana, THC, and cannabidiol (a component of marijuana which does not have the mind-altering effects of THC). Early research shows cannabidiol and its derivatives hold potential promise in additional conditions like drug-resistant epilepsy and some psychiatric disorders (e.g., anxiety, substance use disorders, schizophrenia, and psychosis).
Some states have passed laws, contrary to federal laws, to allow the use of marijuana for medical conditions. Some states have also made the move to decriminalize marijuana use by adults or have similar measures on upcoming ballots. It is unclear what health impact decriminalization of marijuana would have. The experiences of other states and countries that have made these legal changes were varied and unpredictable. The greatest threat would be an increase in adolescent use.

Be cautious if you use marijuana

In the meantime, if you do use marijuana products, do not do so before driving or operating other heavy or dangerous equipment, and stop if you are pregnant. Talk to your doctor about the safety of continued use if you have a heart or lung condition, or are concerned that you might have developed an addiction. Avoid products that are packaged as candy or other edibles if there are children in your household who are more susceptible to a toxic overdose. And talk to your kids about the potential hazards of marijuana, because the risks are particularly high in young people.

Like everything in the marijuana world, the herb’s impact on the lungs is a topic of hot debate. Smoking of any sort is often associated with lung damage. Recent cannabis research, however, is changing the game. While it was once a given that marijuana smoke had the same lung-damaging impact as tobacco, large-scale findings have failed to find a firm correlation. But, there still may be some long-term effects associated with some common smoking methods. The fourth segment of our Healthy Lungs series will go over potential effects of long-term smoking.

Effects of long-term marijuana smoking

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Let’s get one thing clear. Research has put a halt on the idea that smoking marijuana inevitably causes irreversible lung damage. A 2015 study completed by Emory University compared data from marijuana smokers aged 18 to 59 to non-smoking controls. They specifically looked at the ability to exhale. Poor exhalation is a marker of lung disease.
The result? There was no statistical difference between the marijuana smokers and non-smoking controls. Both groups had the same expiratory volume. Here’s what the study concluded:

“Lifetime marijuana use up to 20 joint-years is not associated with adverse changes in spirometric (exhalation strength) measures of lung health.”

The marijuana smokers reported smoking one joint a day. So, one joint a day for up to 20 years is not associated with lung damage. Pretty amazing, right?
The marijuana smokers did experience some negative respiratory side effects, however. Those who smoked joints reported increased coughing and sore throat. These symptoms were avoided by those who used a vaporizer.
Dr. Donald Tashkin, who has been studying the effects of marijuana and tobacco smoking for over 40 years, suggests that bronchitis-like symptoms go away after you stop smoking. He admits that regular marijuana smoking “Causes visible and microscopic injury to the large airways”, but this damage subsides and “Does not appear to lead to significant abnormalities in lung function”.
Additional research from Tashkin has suggested that injury to the lungs corresponds to specific smoking methods. Joints mean greater damage, vaporization means less. Edibles do not damage the lungs.

What about heavy smokers?

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There are a lot of marijuana smokers who puff more than one joint per day. If you’re a heavy user, you might want to invest in a vaporizer. While the actual impact of the marijuana smoke itself has yet to be conclusively determined, chemicals and burning material from rolling papers is thought to contribute to increased inflammation and lung irritation.
With heavy use, this irritation can lead to increased mucus production, inflammation, and chronic bronchitis-like symptoms. In some people, it’s hypothesized that this may lead to increased lung problems. Though, as Tashkin has indicated, the correlation between marijuana smoking and lower respiratory tract infection have yet to be adequately determined. In those who have emphysema , genetics and additional environmental factors may contribute to the problem.
To counter this argument, medical cannabis oil may actually help reduce inflammation and open airways in conditions like COPD and asthma. Yet, if you have either of those conditions, smoking probably won’t be your go-to consumption method.
Allen St. Pierre, director of the National Organization to Reform Marijuana Laws (NORML), puts things into perspective. He told reporters at Think Progress:

“Putting marijuana in your lungs is not the healthiest decision you can make but it’s stark compared to the damage done by tobacco.”

What about lung cancer?

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Thus far, there has been no proven correlation between light to moderate marijuana use and lung cancer. Marijuana smoke does contain some of the same carcinogens as tobacco. Carcinogens are typically found in smoke from burned materials. When you smoke marijuana, however, you’re also taking in THC and CBD.
Both of these cannabinoids are powerful antioxidants, protecting cells and DNA from damaging free-radicals like carcinogens. Though it is not confirmed, these antioxidant properties may help protect your body from smoke-related damage. Cannabinoids also have strong anti-tumor properties. At this point, this hypothesis has not been tested via the standard clinical process in humans.
When it comes to heavy smokers, the exposure to these carcinogens is greater. This is especially true if you prefer smoking blunts or use rolling papers. In general, heavy smokers are thought to face more of a risk of lung damage. According to Tashkin’s study, the evidence is mixed when it comes to the cancer risks of heavy use. He writes:

“Although marijuana smoke contains a number of carcinogens and cocarcinogens, findings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use, although evidence is mixed concerning possible carcinogenic risks of heavy, long-term use.”

Tashkin’s analysis is supported by a review published in the International Journal of Cancer.  Researchers looked at data from 2,159 lung cancer cases and 2,985 healthy controls. They, again, found no correlation between marijuana use and increased lung cancer risk. They conclude:

“Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers, although the possibility of potential adverse effect for heavy consumption cannot be excluded.”

So, what does this research suggest about the long-term impacts of smoking marijuana? Smoking in general causes irritation. This isn’t the healthiest thing in the world. It is unlikely, however, that moderate use will cause any significant negative damage. The research on heavy use is inconclusive. But, switching to a vaporizer or incorporating edibles into your consumption routine can limit potential risks.