Marijuana - what does the science say?
We investigate cannabis and those cure-all claims
“I didn’t inhale”
Bill Clinton, March 29, 1992.
When Clinton spoke those famous sly words about trying marijuana, he was simply reflecting public sentiment. He is a politician. Some 72% opposed legalizing marijuana in the US back then. New figures released just yesterday suggest 67% now support legalization (only 32% oppose). Oh, how times have changed!
To give you an idea of how much public opinion has changed, consider the fact that nearly every US Democratic presidential candidate now supports federal legalization of marijuana. Just a few short years ago there were virtually no mainstream politicians who adopted that position.
Pot. Grass. Mary Jane. Dope. Reefer. Ganja. Whatever the popular name for marijuana, the drug comes from the flowering plant cannabis. Despite public opinion, Cannabis is still considered a Schedule 1 drug in most western nations, placing it in the same category as heroin and ecstasy. Over the last few years, a number of states and countries have legalized cannabis for non-medicinal consumption.
As the fight for legalization rages on, there’s constant public debate about the dangers and benefits of consuming cannabis. Its proponents argue that it’s safe and tout its medicinal properties. Its opponents claim it’s a dangerous, addictive drug that ruins lives.
So what does the latest science say? We gathered more than 50 of the worlds top researchers in neuroscience, public health and medicine to share the facts about cannabis. From whether marijuana is 'harmless' to the many claims made that cannabis can help various health conditions. Members can read the full details of our review here.
As someone who did inhale and now is a father, I learned alot from the experts in this review. Some takeaways for me:
Cannabis potency is increasing and long-term use linked to psychotic disorders.
Occasional use for adults pretty safe in comparison to alcohol and other drugs. But long term use of marijuana is harmful to the brain - particularly teenagers!
Evidence for medical benefits of cannabis are pretty weak - chronic pain and Epilepsy maybe (see answers for anxiety, chronic pain, joint pain, Epilepsy, sleep, Alzheimer’s)
Marijuana is not a ‘gateway drug’ which the US Surgeon General recently claimed. Evidence isn’t strong for that based on our experts.
Members get access to our Cannabis review here and much more. If you want to become a member, you can here:
Keep questioning and always remember, may the facts be with you!
Ben McNeil
Founder, Metafact
The Ancient Chinese Healing Herb
For its supposed healing characteristics, cannabis has been used for thousands of years. The first case recorded was by Chinese Emperor Shen Nung in 2800 BC. From the Indian Hindus to the Greeks, ancient texts have claimed therapeutic benefits for health conditions, including arthritis, depression, amenorrhoea, inflammation, pain, absence of appetite and asthma.
Cannabis is a generic word used to indicate the Cannabis sativa plant's several psychoactive properties. The Mexican word 'marijuana' is often used to refer to cannabis leaves or other crude plant material.
It wasn't until 1841 that cannabis was brought to the West via Irish doctor William Brooke O’Shaughnessy. In the 1920s, western countries started to ban the use of cannabis. The film Reefer Madness was released in the US, demonizing cannabis as a highly addictive drug that caused mental disorder and violence. A year later, US Congress passed the Marijuana Tax Act of 1937 - effectively banning its production, distribution, and use.
In the 1940s, scientists discovered that cannabis contains a set of at least 66 compounds now known as cannabinoids. The main psychoactive cannabinoid in the cannabis plant is trans-DELTA9-tetrahydrocannabinol or "THC". THC is the compound that gets you 'high'. Cannabidiol (CBD) is another major constituent of the cannabis plant but doesn't impact your mental state like THC. Medical marijuana typically refers to CBD extract as it is non-intoxicating. CBD oil is a concentrate of cannabinoids obtained by solvent extraction of the plant or resin.
Medical use of CBD continued with some promising early results around epilepsy. By 1996 California legalized medical marijuana, sparking a trend towards legalization across the western world.
The Consensus
Is recreational marijuana use safe?
There are all sorts of reasons people give for consuming cannabis-based products, but a sizable portion of its users smoke or eat it just for the fun of it. So the first question we posed to our experts was whether recreational marijuana use is actually safe.
Our experts were pretty torn on the question, with several quibbling over the term “safe.” Safe compared to what? “From the standpoint of marijuana as a recreational drug, based on its recreational use to administer THC to get high, it's probably safer than many other drugs used for the purpose (heroin, cocaine, methamphetamine, etc.),” wrote Matthew Springer, a professor of medicine at the University of California, San Francisco.
But that’s not to say that marijuana causes no harm. For one, millions of users consume it via smoke inhalation. “While the psychoactive substance in marijuana is THC rather than nicotine, marijuana smoke is still the result of dried plant material combustion and contains many of the same thousands of chemicals as tobacco smoke, including fine particles that cause cardiovascular morbidity and mortality,” Springer noted.
As with all drugs, the health risks posed by cannabis are somewhat dependent on the frequency of use. Libby Stuyt, an expert from the University of Colorado Denver, wrote that heavy marijuana users are more likely to suffer from suicidal thoughts and “appear to have significant problems with impulse control, concentration, focus, and memory, and say things without really thinking about what they are saying.”
Certain demographics are particularly vulnerable. Several Metafact experts pointed to studies showing that early childhood use can be “associated with lower-than-expected IQ scores and neurocognitive outcomes, including difficulty with attention, impulse control, and executive function.” Research has also shown that those suffering from psychological disorders like schizophrenia are likely to see their symptoms exacerbated by cannabis use.
Several Metafact experts argued that moderate, recreational use of cannabis is mostly safe. “Empirical evidence finds little causal evidence that marijuana increases hard drug use,” noted Luke Chu, an expert from the Victoria University of Wellington. Others questioned the causal relationship between marijuana and bad health outcomes. “Much has been made of the link between cannabis use and psychosis/schizophrenia and whilst it is true that cannabis use can trigger these, it is also likely that these individuals are predisposed to developing these conditions,” wrote Gareth Pryce, an expert from Queen Mary University of London. He cited stats showing that incidents of schizophrenia in the UK have remained relatively stable over a period of decades when cannabis use measurably increased.
And of course there are the potential medicinal benefits offered by cannabis. But we’ll get to those in a few moments.
The Consensus
Does marijuana harm the brain?
Let’s dive a little bit deeper on the alleged health impacts of cannabis on the human brain. Specifically, does it affect a person’s cognitive abilities, both in the short and long term?
“YES, it can be harmful, especially if used during the vulnerable period of adolescence,” wrote Justine Renard, a neuroscientist from the University of Western Ontario. She pointed to studies showing that use of THC before the age of 17 “can increase the risk of developing important cognitive deficits and psychiatric disorders in adulthood, including anxiety, depression, and schizophrenia.”
Indeed, a few experts pointed to studies showing links between marijuana use and psychotic disorders. “Statistically, there is a robust but moderate association between heavy cannabis use as a youth and the development of psychotic disorders in adulthood,” noted Nehal Vadhan, an expert from Zucker School of Medicine at Hofstra-Northwell. “The likelihood is strongest when: 1) the cannabis a) is very potent, b) starts @ a very young age, and c) is uninterrupted; and the individual had a preexisting risk for a psychotic disorder already.”
Unfortunately, we still don’t know why the two are linked. “Cannabis is not thought to be causal in the development of psychosis by itself - it combines with a number of other risk factors which we still need to understand better,” wrote Nadia Solowij, an expert from the University of Wollongong. “But for some, even single or minimal use of cannabis can trigger a psychosis that may never have developed otherwise, and for young people in particular this is a devastating outcome.”
Some Metafact experts again compared marijuana use to other potentially harmful drugs and deemed it relatively safe. “Yes, THC acts on these important systems but that does not mean the brain is ‘harmed,’” argued Charles Ksir, a professor of psychopharmacology from the University of Wyoming. “Some of the same people who make this argument will prescribe drugs that have profound influences on serotonin, GABA, dopamine, etc and they seem to be less concerned about the long-term consequences of those drug exposures during development, for reasons that elude me.”
It seems clear that pregnant women should steer clear from the drug. Justine Renard pointed to studies showing potential long term cognitive impairment caused from prenatal exposure. “It is important to emphasize that THC is able to cross the placental barrier and to be secreted in breast milk,” she wrote.
But if you’re over the age of 18, the long term impact of cannabis use seems to be limited. Matthijs Bossong, an expert from University Medical Center Utrecht, cited data showing that the negative effects “attenuated with prolonged abstinence, suggesting recovery from the residual cognitive impact of cannabis use.”
The Consensus
Is marijuana addictive?
There’s been a longstanding debate among the general public over whether marijuana is addictive. It’s likely that at some point you’ve heard the claim from a lay person that it isn’t.
Of course the word “addictive” can mean different things, referring to both physiological and psychological effects. It’s fairly clear that frequent users of THC develop a tolerance from the drug, and they can also suffer from withdrawal symptoms. Ole Rogeberg, an expert from Ragnar Frisch Centre for Economic Research, cited a study in which subjects were given THC capsules every four hours. “They report a rapid tolerance development (within a day or two), and a clear withdrawal syndrome, likened by some of the participants to the flu,” he wrote. “Some reported sleep disturbances for up to 7 days following cessation.”
One expert compared it to alcohol, a substance that doesn’t cause addiction for the vast majority of its users but can induce dependence for some. “There are ... millions of people who use cannabis in any of its presentations as a form of relaxation after a day of resolving their conflicts,” wrote Eduardo J. Pedrero Pérez, an expert from Madrid Health. “It can also be combined with other sources of reinforcement (e.g. music, social contact, watching movies), so that it does not isolate the subject, but rather reduces his or her tension. Or it may continue to be limited to certain playful moments, in the company of others, without affecting the rest of the subject's behavioural repertoire.” Thiago Pianca, an expert from Universidade Federal do Rio Grande do Sul, cited research suggesting that “just about 7-10% of users will become addicted.”
The Consensus
Does cannabis use have medicinal benefits?
Read all the claims here for pain, anxiety, sleep, MS, Epilepsy etc..
What about all the health claims around marijuana? After all, plenty of countries and states have passed medical marijuana laws that allow the purchase of the drug with a prescription.
Unfortunately, because of the longstanding laws against marijuana distribution, the studies around its use have been limited in size and scope. Most importantly, government funding of research is low and therefore most of the research is funded by the industry. So many of the Metafact experts relating to cannabis have declared conflict of interests.
There is mixed evidence that cannabis use can have medicinal benefits. Let’s start with anxiety relief - it's uncertain according to 5 experts so far. CBD to help anxiety is "likely but not yet proven" says Professor Andrea Giuffrida from University of Texas Health and "more controlled clinical studies needed".
What about relieving pain? There seems more of science to back this up according to 8 experts. “There are numerous studies that show that cannabis reduces pain and improves quality of life of patients with chronic pain,” wrote Alex Bekker, an expert from Rutgers New Jersey Medical School. “For example, a systematic review of randomized controlled clinical trials (766 patients) assessing salutary effects of cannabinoid in treating chronic non-cancerous pain showed significant analgesic effect of these treatment.”
And does Cannabis help with sleep? Sort of. “On the one hand, patients using medical cannabis for different indications, including pain, post-traumatic stress disorder, Parkinson's disease and other conditions are reporting an improvement in their sleep following cannabis use,” wrote Ran Abuhasira, an expert from Ben-Gurion University of the Negev. “On the other hand, sleep disturbances are among the most frequent complaints of cannabis withdrawal and are a major cause for continued use after attempts to quit.”
The Consensus
Is marijuana a 'gateway drug'?
U.S. Surgeon General Jerome Adams recently sparked controversy when he posted a Twitter video in which he made the claim that marijuana acts as a so-called “gateway drug” to harder drugs like cocaine and heroin. This is a claim that’s long been held by marijuana legalization opponents, but is there any science to back it up?
Not really. Luke Chu, an expert from Victoria University of Wellington, noted studies showing that “while marijuana use had increased after the passage of medical marijuana laws, use of other substances like cocaine and heroin did not increase.” In fact, “medical marijuana states experience a relative decrease in opioid addictions and opioid overdose deaths.”
Why does the “gateway drug” myth exist? Mostly because marijuana opponents take a correlation between marijuana and hard drug use and draw a causal relationship where none exists. “A minority of marijuana users will go onto to use other illegal substances but the vast majority will not use the drug more than a few times or will not undertake any further experimentation,” wrote Stuart Taylor, and expert from Liverpool John Moores University.
One possible “gateway” that some Metafact experts suggested was the idea that, because marijuana is illegal in most states, purchasing it involves associating with drug dealers, who may end up pushing the buyer into experimenting with harder drugs. “Legalizing cannabis would actually weaken this one area where the 'gateway' effect may operate - this was the rationale behind the Dutch 'coffeeshop' system which aimed to separate the markets for 'soft' drugs (i.e., cannabis) and 'harder' drugs,” wrote Gary Potter, an expert from Lancaster University.
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