Clearing the Smoke: The Science of Cannabis

Montana PBS’s new documentary, Clearing the Smoke, reveals how cannabis acts on the brain and in the body to treat nausea, pain, epilepsy and potentially even cancer.
Extensive interviews with patients, doctors, researchers and skeptics detail the promises and the limitations of medicinal cannabis. Even though the video has an American perspective, marijuana use is illegal throughout many countries of the world for reasons that are not clear.
This video is important because it mainly investigates the scientific basis underlying the medical benefits of marijuana use instead of focusing on the social, political and legal hysteria that have been attached to it.

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  1. The benefits of medical cannabis far outweigh the risks, even when smoked. It has antibiotic properties and has been proven to kill certain types of cancer cells.

  2. According to the United States Department of Health and Human Services, there were 455,000 emergency room visits associated with cannabis use in 2011. These statistics include visits in which the patient was treated for a condition induced by or related to recent cannabis use. The drug use must be “implicated” in the emergency department visit, but does not need to be the direct cause of the visit. Most of the illicit drug emergency room visits involved multiple drugs.[42] In 129,000 cases, cannabis was the only implicated drug.[43][44]

    A 2013 literature review said that heavy, long term exposure to marijuana may have biologically-based physical, mental, behavioral and social health consequences and may be “associated with diseases of the liver (particularly with co-existing hepatitis C), lungs, heart, and vasculature”.[45] It is recommended that cannabis use be stopped before and during pregnancy.[46]


    THC, the principal psychoactive constituent of the cannabis plant, has low toxicity, the dose of THC needed to kill 50% of tested rodents is extremely high. Acute effects may include anxiety and panic, impaired attention, and memory (while intoxicated), an increased risk of psychotic symptoms, and possibly and increased risk of accidents if a person drives a motor vehicle while intoxicated.[47] Psychotic episodes are well-documented and typically resolve within minutes or hours. There have been few reports of symptoms lasting longer.[48][49] Cannabis has not been reported to cause fatal overdose.[50] Studies have shown that cannabis use causes impairments in memory that persist beyond short-term intoxication.[51]


    There has been a limited amount of studies that have looked at the effects of smoking cannabis on the respiratory system.[52] Chronic heavy marijuana smoking is associated with coughing, production of sputum, wheezing, and other symptoms of chronic bronchitis.[47]Regular cannabis use has not been shown to cause significant abnormalities in lung function.[53] Short-term use of cannabis is associated with bronchodilation.[54]


    Cannabis smoke contains thousands of organic and inorganic chemical compounds. This tar is chemically similar to that found in tobacco smoke,[55] and over fifty known carcinogens have been identified in cannabis smoke,[56] including; nitrosamines, reactive aldehydes, and polycylic hydrocarbons, including benz[a]pyrene.[57] As of 2015, there is no consensus regarding whether cannabis smoking is associated with an increased risk of cancer.[58] Light and moderate use of cannabis is not believed to increase risk of lung or upper airway cancer. Evidence for causing these cancers is mixed concerning heavy, long-term use. In general there are far lower risks of pulmonary complications for regular cannabis smokers when compared with those of tobacco.[53] Combustion products are not present when using a vaporizer, consuming THC in pill form, or consuming cannabis foods.


    There is serious suspicion among cardiologists, spurring research but falling short of definitive proof, that cannabis use has the potential to contribute to cardiovascular disease.[59] Cannabis is believed to be an aggravating factor in rare cases of arteritis, a serious condition that in some cases leads to amputation. Because 97% of case-reports also smoked tobacco, a formal association with cannabis could not be made. If cannabis arteritis turns out to be a distinct clinical entity, it might be the consequence ofvasoconstrictor activity observed from delta-8-THC and delta-9-THC.[60] Other serious cardiovascular events including myocardial infarction, stroke, sudden cardiac death, and cardiomyopathy have been reported to be temporally associated with cannabis use. Research in these events is complicated because cannabis is often used in conjunction with tobacco, and drugs such as alcohol and cocaine.[61] These putative effects can be taken in context of a wide range of cardiovascular phenomena regulated by theendocannabinoid system and an overall role of cannabis in causing decreased peripheral resistance and increased cardiac output, which potentially could pose a threat to those with cardiovascular disease.[62] There is some evidence from case reports that cannabis use may provoke fatal cardiovascular events in young people who have not been diagnosed with cardiovascular disease.[63]


    A 2013 review comparing different structural and functional imaging studies showed morphological brain alterations in long-term cannabis users which were found to possibly correlate to cannabis exposure.[64] A 2010 review found resting blood flow to be lower globally and in prefrontal areas of the brain in cannabis users, when compared to non-users. It was also shown that giving THC or cannabis correlated with increased bloodflow in these areas, and facilitated activation of the anterior cingulate cortex and frontal cortex when participants were presented with assignments demanding use of cognitive capacity.[65] Both reviews noted that some of the studies that they examined had methodological limitations, for example small sample sizes or not distinguishing adequately between cannabis and alcohol consumption.[64][65] A 2011 review found that cannabis use impaired cognitive functions on several levels, ranging from basic coordination to executive function tasks.[66] A 2013 review found that cannabis users consistently had smaller hippocampi than nonusers, but noted limitations in the studies analyzed such as small sample sizes and heterogeneity across studies.[67] A 2012 meta-analysis found that the effects of cannabis use on neurocognitive functions were “limited to the first 25 days of abstinence” and that there was no evidence that such use had long-lasting effects.[68]


    It is not clear whether cannabis use affects the rate of suicide.[50]

    Chronic use

    Effects of chronic use may include bronchitis, a cannabis dependence syndrome, and subtle impairments of attention and memory. These deficits persist while chronically intoxicated.[47] There is little evidence that cognitive impairments persist in adult abstinent cannabis users.[69] Compared to non-smokers, people who smoked cannabis regularly in adolescence exhibit reduced connectivity in specific brain regions associated with memory, learning, alertness, and executive function.[44] A study has suggested that sustained heavy, daily, adolescent onset cannabis use over decades is associated with a decline in IQ by age 38. No effects were found in those who initiated cannabis use later, or in those who ceased use earlier in adulthood.[63]

    Tolerance and withdrawalMain article: Cannabis dependence

    Cannabis usually causes no tolerance or withdrawal symptoms except in heavy users. In a survey of heavy users 42.4% experienced withdrawal symptoms when they tried to quit marijuana such as craving, irritability, boredom, anxiety and sleep disturbances.[70]About 9% of those who experiment with marijuana eventually become dependent. The rate goes up to 1 in 6 among those who begin use as adolescents, and one quarter to one-half of those who use it daily according to a NIDA review.[44] A 2013 review estimates daily use is associated with a 10-20% rate of dependence.[25] The highest risk of cannabis dependence is found in those with a history of poor academic achievement, deviant behavior in childhood and adolescence, rebelliousness, poor parental relationships, or a parental history of drug and alcohol problems.[71] Cannabis withdrawal is less severe than withdrawal from alcohol.[72]

    Motor vehicle crashes

    A 2012 meta-analysis found that cannabis use was associated with an increased risk of being involved in a motor vehicle crash.

  3. they say they have no money to fund “proper” research…so you are trying to tell me that a company like pfizer cant fund a research … think about it … they can have a best drug with the least side effects !

    also … the lumber buisness will basicly go out of buissnes.
    watch the union !! really good one !

    ps im stoned 🙂 !!!

  4. this is the best documentary on cannabis…

  5. i have been smoking pot since i was 13 after trying it for my chronic back pain(no pun intended) and found it better and safer than any pain relever and doctors want me to stop and take perscirption pain killers can you believe that the doc says its safer to take oxys than smoke weed what an idiot

  6. Isn’t our Government the greatest?

  7. This Is the most informational video! And Dr. Henseld looks high as fuck!(dude in blue sweater vest thingy)

  8. scumbag reporter:  conceals face, shows self portrait

  9. They talk about the fact that marijuana has an addictive potential…. What about Oxycontin, Morphine and all those other pills that they gladly sell you with prescriptions and make you totally addicted? The situation with marijuana is ridiculous. It is not that addictive and when it is, it is from a psychological point of view. It has no serious withdrawal symptoms. It is effective against nausea, increases appetite, induces a well being feeling and relaxation. I am shocked and appalled that it is classified as a category one drug with LSD AND HEROIN!!! Yet, your doctor can write you a prescription for level II drugs such as COCAINE????? Outrageous! Way to go, America! And all that because hemp had a huge potential and some lobbies didn’t want to let it go.. so they basically made up a horrible reputation for this remedy which has been used for millennia! Have you ever seen someone high as a kite become violent? Give me a break!

    • it may be better to say dependent and not addicted, there is a big difference between these two terms. I know because I am dependent on morphine and methadone for serious nerve damage. The difference is that people who are dependent miss doses and at times refuse to take the meds until they are too sick and have no choice, usually in a ER due to the complications from not taking these meds when they really are needed. Addicted people watch time and take the meds as often as hey can… or more often so they run out before the next script is available. You see, after taking these meds to get back to a state where you are no longer screaming, odd how you may not hear that it is you doing the screaming,.. but once stable I always stop taking the stuff. This makes things much worse but I really do not like having my life tied to the medical industry or any medication. Pot does not work to stop my kind of pain/illness but if it did… I would not use it either. I am told by MDs I am just an odd person and to stop tearing my body up. Easy for them to say as it is I being treated like crap by the society and pharms when I show up to fill my scripts.

    • Well actually they can prescribe you “Sativex” which is Marijuana. Why you think the government’s made it schedule 1? Because the government is now your new weed dealer…

    • TESTIFY !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  10. Fascinating watch, the one issue is the narrator constantly cutting off people talking during their interviews and then running off to do show something else, I wish they had made those feel more like natural pauses then interruptions of the people talking  and saying something, feels like they were being pushed aside.

  11. one of my main reasons for trying to move to a state where med is legal. it helps me in so many ways other than just my insomnia, anxiety, head aches and chronic pain. if its not legal in the next 5 years i will lose all hope in humanity…well more than i have already….

  12. So, I watched and then spent 3 hours reading the FDA manifesto where I cannot find any evidence why MJ is regulated under the FDA and not the Internal Revenue Code of 1986 where distilled spirits, wine, malt beverages, or tobacco are regulated – let alone as schedule 1!!!  The definitions and classifications are not aligned with any other chemically engineered PRODUCT.  This is a plant!!!
    Here is the link if you’ve got some down time…

    Or you can try to search the site where you will find endless pages of drug testing kit information.  Perhaps they’ve used the FDA classification for purely enforcement purposes and now we’re in too deep???  If the FDA keeps it, the pharma companies will control it – if we get it out of the FDA then there will be opportunity to research it, produce it, distribute it, regulate the distribution and yes, TAX IT!

  13. receptor need a natural weed not a man made pill to make belive (money)……………………………………………………………………..

  14. The most important thing about this documentary is that it is specific to people with classified medical illnesses and it should not be used in order to condone excessive cannabis use. The primary reason that cannabis is not illegal is it that it generally takes away our motivation to engage in capitalistic ventures, subsequently, eradicating this hideous social structure, personally I do not see why that is a bad thing. Since capitalism destroys itself every few decades anyway.

    One flaw of the documentary was the lack of cross cultural research. For example, in Holland cannabis is legal, therefore, one could assume they have many researches into the medical affects of cannabis. Nonetheless, it is a convincing and inspirational documentary.

  15. Not sure schizoid events are that common in cannabis use , but I am sure it can fuel anxiety in anxious people. It can also focus attention to pain rather than release it. There is some evidence that some substrates of chemicals in the plant can relieve inflammation and relieve nausea but rather than use the whole herb maybe they should isolate the useful substrates that can relieve the patient without impairment.

    • People who already have schizophrenia are clearly advised not to smoke marijuana as it may induce and episode, I think its above a 40% chance after a month. There is almost no risk to healthy users.

      They’ve tried substrate extracts, however the drugs (available so far) are almost ineffective compared to simply smoking the plant.

      Its hardly an impairment. Its very enjoyable.

      • The effects of paranoia are mostly caused by people being scared to be caught. I have never been paranoid when high unless I am afraid somebody knows. Why is that? It’s because we don’t trust people around us due to the fact you can get in trouble.

        If Obama ever grows a pair maybe he’ll actually have a side issue in his candidacy to regulate cannabis. I hate how much money is wasted to create new drugs and fund new laboratories with the sole function to recreate effects of things that are already in abundance…

        What pisses me off even more is the fact you can buy the plants to create heroin/opium and mescaline all legally from Wal-Mart. What is even worse is that you can have a papaver plant just oozing the sap in your front yard. Even Datura is legal. This is so ridiculous.

        I hate how that one asshole doctor had his whole entire basis for it remaining illegal was because it’s illegal. Is no one even hearing that?

        I fucking hate republicans. There are more than two parties. There’s the republicans, then everybody who can debate reasonably who can have changes of opinion aka liberal aka democrat. I hate having to vote for somebody the wealthiest of democrats pick for us. How about somebody who isn’t worried about relating to the average guy, because they don’t see people as different. Maybe somebody who is good at math, science, arts, history and philosophy, not how to make a profit. Who gives a shit if the government isn’t making money, it’s money you people pay that you shouldn’t expect back. That money is paying for the shit you see going on, do something or stop paying it.

        • From a personal perspective, I’m not sure how much of it is out of fear, and how much is out of chemical imbalance. Lemme explain..

          I smoked for about 1.5 years. Most of that time, I was in the military. For the bulk of that time, knowing that random piss tests could be called for, knowing that people in my unit didn’t like me (and would turn me in if they found out I smoked), etc.. I never had a bad experience. I really, really liked being high.

          The problems arose when I was over seas. A buddy of mine got some weed before he went on leave to Japan. I talked him into giving me a tiny bit, enough for 1 high. When he gave me the weed, I noticed some crystals on the bud.. something I’d never seen before. Now, I don’t know if that was just “good weed”, or if it was laced, or what.

          The first hit was pretty damn obvious. My eyes instantly got that “wow, I’m baked” feeling. I decided to only have one more hit.. then I drifted off on lots of tangent thoughts.. then I saw the weed in a can in my hand and thought “hey, look.. weed.. I should take a hit”. I never got so stoned so fast in my life.

          Now, granted.. I was on base, over seas, and sneaking around a construction site and worried that I might be seen. There’s a grounds for paranoia there, yes? But my mind was racing like never before. I managed to toss the can (evidence) and was feeling pretty good. I figured I’d go to the club and listen to the band for a little bit. Mind you, I’d been smoking for over a year and a half.. this should have been no issue. Also note, I only had 2 hits.

          As I entered the club I realized that I must have the stink on me. Yet, it was too late, I was in. I figured I had to go sit down or it would be odd that I walked in and walked out. As I walked down the small isle in this small room, I saw people turn and look at me. As they did, their faces floated off their bodies and toward me, saying “yeah, this fucker is stoned.. we got him”. Talk about paranoid.

          I sat down and tried to “act normal”.. but I kept nodding off like I might be totally drunk. It was a very disconcerting experience at that point. I finally forced myself to get up and leave. I headed back to the barracks and flopped down in my bed and started playing a tape (yeah, it was that long ago). Pink Floyd, Money.

          Well, after about what seemed an hour of watching vivid animations behind my closed eyes, I had to turn off the music (it was actually less than one song, but it was damn disconcerting.. hallucinating with your eyes closed).

          Ever since then, I get a bit “off” when I smoke. I’d like to call it paranoia, but others actually hear the “odd things” I hear… see the odd things I see. Either they are a bit nuts too, or I’m really really nuts, or there’s some kind of spiritual good/evil thing going on that I don’t want to accept as a point of fact. … from my understanding, it may well be a bit of a psychotic or schizophrenic break.

          The problem with Schizophrenia is that you either have it or don’t. Pot doesn’t cause it, but you might not have it to a degree that it’s noticeable under normal conditions, but smoking pot might break that thin veil and cause the disease to manifest. I’ve never been tested, MRI’d, or diagnosed with it.. but it sure scared the shit out of me enough that I quit smoking and haven’t again for 20 years.

          Now.. if it becomes legal at the federal level, I’ll probably try it again. I know that I have _nothing_ to fear (it’s 100% legal in this trial), so that unconscious knowledge might be all it takes for me to be back to really enjoying being high. The complication for me is, I have physical pain problems (neurological) that may benefit from cannabis. It would suck if I have chemical/mental issues that prevent the use of it for pain management.

        • I agree with your points and am a huge liberal. But the democrats have been also nearly as weak as the republicans, and many republican libertarians have really helped to show how much a sham keeping weed is illegal. 

          I swear Canada would of made weed legal if it wasn’t for the states, well atleast under the old liberal gov.
          I’d like to add the main reason weed is illegal is legal drug companies and tobacco/booze companies. They like to be the only ones in the game to get you buzzed, and have the money to prevent it from happen. 

          Whats crazy is weed is most likely far safer less harmful then the legal drugs/tobacco/booze. 

  16. Negative side effects??.. What was the alternative?. Death..geeez, get a grip dr. Voth

  17. A schedule 1 drug which has never killed anyone?  The illegality of cannabis is ridiculous and a waste of money. Dr. Voth is clearly driven by negative opinion – his best argument against medical marijuana is that is may have some negative side effects in some people? He has no business advising anyone and is clearly behind the curve.