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Marijuana's official designation as a Schedule 1 drug— something with "no currently accepted medical use" — means it's pretty tough to study.
Yet a growing body of research and numerous anecdotal reports link cannabis with several health benefits, including pain relief and the potential to help with certain forms of epilepsy. In addition, researchers say there are many other ways marijuana might affect health that they want to better understand.
Along with several other recent studies, a massive report released this year by the National Academies of Sciences, Engineering, and Medicine helps sum up exactly what we know— and what we don't — about the science of weed.
Marijuana can make you feel good.
AP Photo/Brennan Linsley
One of weed's active ingredients, tetrahydrocannabinol, or THC, interacts with the brain's reward system, the part primed to respond to things that make us feel good, like eating and sex.
When overexcited by drugs, the reward system creates feelings of euphoria. This is also why some studies have suggested that excessive marijuana use can be a problem for some people — the more often you trigger that euphoria, the less you may feel during other rewarding experiences.
In the short term, it can also make your heart race.
REUTERS/Jorge Dan Lopez
Within a few minutes of inhaling marijuana, your heart rate can increase by between 20 and 50 beats a minute. This can last anywhere from 20 minutes to three hours, according to the National Institute on Drug Abuse.
The new report found insufficient evidence to support or refute the idea that cannabis might increase the overall risk of a heart attack. The same report, however, also found some limited evidence that smoking could be a trigger for a heart attack.
Marijuana's effects on the heart could be tied to effects on blood pressure, but the link needs more research.
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In August, a study published in the European Journal of Preventive
Cardiology appeared to suggest that marijuana smokers face a threefold
higher risk of dying from high blood pressure than people who have
never smoked — but the study came with an important caveat: it
defined a "marijuana user" as anyone who'd ever tried the drug.
Research suggests this is a poor assumption — and one that could
have interfered with the study's results. According to a recent survey,
about 52% of Americans have
tried cannabis at some point, yet only 14% used the drug at least
once a month.
Other studies have also come to the opposite conclusion of the
present study. According to the Mayo Clinic, using cannabis could
result in decreased— not increased — blood pressure.
So while there's probably a link between smoking marijuana and
high blood pressure, there's not enough research yet to say that
one leads to the other.
Weed may also help relieve some types of pain.
Pot contains cannabidiol, or CBD, a chemical that is not responsible
for getting you high but is thought to be responsible for many of
marijuana's therapeutic effects.
Those benefits can include pain relief or potential treatment for certain
kinds of childhood epilepsy.
The new report also found conclusive or substantial evidence —
the most definitive levels — that cannabis can be an effective treatment
for chronic pain, which could
have to do with both CBD and THC. Pain is also "by far the most common"
reason people request
medical marijuana, according to the report.
Pain relief could include the discomfort of arthritis.
Robert Johnson for Business Insider
One of the ways scientists think marijuana may help with pain is by
reducing inflammation, a component of illnesses like rheumatoid arthritis.
A preliminary 2005 study of 58 patients with RA, roughly half of
whom were given a placebo and roughly half of whom were given
a cannabis-based medicine called
Sativex, found "statistically significant improvements in pain on
movement, pain at rest, quality of
sleep" for patients on Sativex.
Other studies testing other cannabinoid products and inhaled marijuana
have shown similar pain-relieving effects, according to the report.
Individuals with inflammatory bowel disease may
also find some relief.
Reuters/Lucy Nicholson
Some people with inflammatory bowel diseases like Crohn's and ulcerative
colitis could also benefit from marijuana use, studies suggest.
A 2014 paper, for example, describes two studies of people with chronic
Crohn's. Half were given the drug and half got a placebo. That study showed
a decrease in
symptoms in 10 of 11 subjects using cannabis, compared with just four
of 10 on the placebo. But
when the researchers did a follow-up study using low-dose CBD,
they saw no effect in the patients.
Researchers say that, for now, we need more research before
we'll know whether cannabis can help with these diseases.
Marijuana may also be helpful in controlling epileptic
seizures.
A drug called Epidiolex, which contains CBD, may be on its way to
becoming the first of its kind to win approval from the Food and Drug
Administration for the treatment
of rare forms of childhood epilepsy.
The company that makes it, GW Pharma, is exploring CBD for its
potential use in people with Dravet syndrome, a rare form of childhood-onset epilepsy that is
associated with multiple types of seizures.
In March, the company came out with phase three trial data that
showed the drug had some positive results.
But it can also mess with your sense of balance.
Thomson Reuters
Marijuana may throw off your balance, as it influences activity in the cerebellum and basal ganglia, two brain areas that help regulate balance, coordination, reaction time, and posture.
And it can distort your sense of time.
Feeling as if time is sped up or slowed down is one of the most commonly
reported effects of using marijuana. A 2012 paper sought to draw some
solid conclusions from studies on those anecdotal reports, but it was
unable to do so.
"Even though 70% of time estimation studies report overestimation,
the findings of time production and time reproduction studies remain
inconclusive,
" the paper said.
In a 1998 study that used magnetic resonance imaging (MRI) to focus
on the brains of volunteers on THC, the authors noted that many
had altered blood flow to the
cerebellum, which most likely plays a role in our sense of time.
Limitations on what sort of marijuana research is allowed make it
particularly difficult to study this sort of effect.
Weed can also turn your eyes red.
Since weed makes blood vessels expand, it can give you red eyes.
And you'll probably get the munchies.
A case of the munchies is no figment of the imagination — both casual and
heavy marijuana users tend to overeat when they smoke.
Marijuana may effectively flip a circuit in the brain that is normally
responsible for quelling the appetite, triggering us to eat instead, according
It all comes down to a special group of cells in the brain that are normally
activated after we have eaten a big meal to tell us we've had enough.
The psychoactive ingredient
in weed appears to activate just one component of those appetite-
suppressing cells,
making us feel hungry rather than satisfied.
Marijuana may also interfere with how you form memories.
Marijuana can mess with your memory by changing the way your brain
processes information, but scientists still aren't sure exactly how this happens. Still, several
studies suggest that weed interferes with short-term memory, and
researchers tend to see
more of these effects in inexperienced or infrequent users than
in heavy, frequent users.
Unsurprisingly, these effects are most evident in the acute sense — immediately after use, when people are high.
According to the new NASEM report, there was limited evidence
showing a connection between cannabis use and impaired academic
achievement, something that
has been shown to be especially true for people who begin smoking
regularly during adolescence.
(That has also been shown to increase the risk for problematic use.)
Importantly, in most cases, saying cannabis is connected to an
increased risk doesn't mean marijuana use caused that risk.
In some people, weed could increase the risk of depression.
Scientists can't say for sure whether marijuana causes depression or
depressed people are simply more likely to smoke. But one study from the Netherlands suggests
that smoking weed could raise the risk of depression for young people
who already have a special serotonin gene that could make them
more vulnerable to depression.
Those findings are bolstered by the NASEM report, which found
moderate evidence that cannabis use was linked to a small increased
risk of depression.
And it may also increase the risk of developing schizophrenia.
Matilde Campodonico/AP
The NASEM report also found substantial evidence of an increased
risk among frequent marijuana users of developing schizophrenia
— something that studies have
shown is a particular concern for people at risk for schizophrenia
in the first place.
Regular marijuana use may also be connected to an
increased risk of social anxiety.
REUTERS/Jason Redmond
Researchers think it's possible that CBD might be a useful treatment for
anxiety disorders, and that's something that several institutions are
currently trying to study.
The recent report suggested that evidence of a link between marijuana
and an increased risk of most anxiety disorders was limited.
However, the authors wrote that there is moderate evidence that regular
marijuana use is connected to an increased risk of social anxiety. As in
other cases,
it's hard to know whether marijuana use causes that increase or
people use marijuana
because of an increased risk of social anxiety.
It's worth noting that marijuana has likely gotten
stronger since the 1980s, and that its ratio of THC to
CBD has changed as well.
REUTERS/Mario Anzuoni/File Photo
The THC content of marijuana across the US has tripled since 1995,
according to a large recent study in which researchers reviewed
close to 39,000 samples of cannabis.
While THC levels hovered around 4%, on average, in 1995, they
skyrocketed to
roughly 12% in 2014.
Meanwhile, the CBD content in marijuana — the part that's responsible
for many of the drug's therapeutic effects— has dropped, the
researchers found, shifting the
ratio of THC to CBD from 14:1 in 1995 to about 80:1 in 2014.
Still, tracking THC potency over time can be tricky. The older a weed
sample gets, the more its THC appears to degrade. How it is stored
matters too. These two
barriers could be interfering somewhat with the metrics on pot's potency.
Most importantly, regular weed use is linked with
some specific brain changes — but scientists can't
say for sure whether one causes the other.
Jason Redmond/Reuters
In a recent study, scientists used MRI brain scans to get a better picture
of the brains of adults who have smoked weed at least four times a week
for years.
Compared to people who rarely or never used the drug, the long-term
users tended to have a smaller orbitofrontal cortex, a brain region
critical for processing
emotions and making decisions. But they also had stronger
cross-brain connections, which scientists
think smokers may develop to compensate.
Still, the study doesn't show that smoking pot caused certain regions
of the brain to shrink; otherstudies suggest that having a smaller
orbitofrontal cortex in the
first place could make someone more likely to start smoking.
Most researchers agree that the people most susceptible to brain
changes are those who begin using marijuana regularly during adolescence.
Marijuana use affects the lungs but doesn't seem to
increase the risk of lung cancer.
Silvia Izquierdo/AP
People who smoke marijuana regularly are more likely to experience
chronic bronchitis, according to the report. There's also evidence
that stopping smoking relieves these symptoms.
Yet perhaps surprisingly, the report's authors found moderate evidence
that cannabis was not connected to any increased risk of the lung
cancers or head and neck cancers associated with smoking cigarettes.
Some athletes think marijuana could be used
in ways that might improve certain types of
physical performance.
Andy Cross/The Denver Post via Getty Images
Some athletes, especially in certain endurance and adventure sports,
say marijuana use can boost their athletic performance. This may be because of anti-inflammatory
or pain-relieving effects that make it easier to push through a long
workout or recover from one.
At the same time, there are ways that marijuana could impair athletic
performance, since it affects coordination and motivation, and dulls
the body's natural recovery process.
Without more research, it's hard to know how marijuana affects athletic
performance.
There's evidence that marijuana use during pregnancy
could have negative effects.
10 Face/Shutterstock
According to the new NASEM report, there's substantial evidence showing
a link between prenatal cannabis exposure — when a pregnant woman
uses marijuana —
and lower birth weight. There was limited evidence suggesting that
using marijuana during pregnancy
could cause complications and increase the risk that a baby would
have to spend time in a neonatal
intensive care unit.
There are still so many questions about how marijuana
affects the body and brain that scientists say far more
research is needed.
Shutterstock
Based on the available evidence and conversations with researchers,
there are good reasons to think marijuana has potentially valuable medical
uses. At the same time,
we know that, as with any substance, not all use is risk-free.
More research is needed to figure out how to best treat the conditions that cannabis can help and how to minimize any risks associated with medical or recreational use.
Staci Gruber, an associate professor of psychiatry at Harvard Medical
School and the director of the Marijuana Investigations for Neuroscientific
Discovery program at
McLean Hospital, told Business Insider that marijuana research is
essential in determining
"how best we can use it, what are the safest ways, and what are the real risks."
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