Marijuana: What We Know About Weed’s Benefits and Side Effects

Written by

Lee Johnson

Lee Johnson is the senior editor at CBD Oracle, and has been covering science, vaping and cannabis for over 10 years. He has a MS in Theoretical Physics from Uppsala...

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It can be challenging to find good information on cannabis. On one side, you have a kind of knee-jerk prohibition reaction, where people are worried about the side effects of marijuana and skeptical of its potential benefits even in the face of good evidence. And on the other you have people – like us – who generally like cannabis but can sometimes be prone to underplaying potential risks or negative effects.

But as a consumer, what you really need is the facts about the pros and cons of cannabis (marijuana), with the benefits and side effects assessed fairly and reasonably. For me, the benefits are well worth the side effects, but you might not agree, and most importantly, you can make the decision for yourself.

So if you’re looking for the facts without the spin, this is the article for you.


  • Marijuana is cannabis that’s particularly high in THC. Cannabis gets you “high” – so you’ll feel happy, giggly, relaxed and talkative
  • It can affect short-term memory, make you feel dizzy or sick, or even paranoid
  • Cannabis contains 540 chemical compounds, 113 of which are called cannabinoids, the majority of the plant is made up of just 2 – THC and CBD. Most side effects are attributed to THC. 
  • High amounts of THC can induce mental health issues such as anxiety and mental fragility in some people, while high CBD strains reduce these symptoms
  • As a medicine it could help with chronic pain, some forms of epilepsy, multiple sclerosis, nausea and vomiting, anxiety and much more
  • Regular long-term use probably increases your risk of mental health issues (for high THC strains), may pose some risk to your lungs and could potentially cause cancer (if smoked).
  • Vaporizing or eating cannabis reduces the risks to your lungs, but in any case they are less than the risk from tobacco.

Recreation is Different From Medication

Recreational marijuana plant

One key point to note before we get into the details of the benefits and downsides of marijuana is that what you’re using it for is very important.

If you’re a recreational marijuana user, some of the things considered “side effects” of cannabis in a medical context are part of what you’re looking for.

On the other hand, as a medical marijuana user the benefits are more about the effectiveness for treating your condition rather than the subjective effects.

So here we’ll aim to separate these two purposes as much as possible.

Long Term Risks are Different From Side Effects

When you say side effects in a medical context, it essentially means relatively short-term consequences of taking the medicine.

For example, you might get a dry mouth or notice an alteration in your appetite within a few hours, although that wasn’t the intention of the treatment.

Whereas long term risks of a medication tell you about the possible consequences if you keep using it for a long time.

Again, this distinction is important, but we’ll be discussing both in this article.

For Recreational Users, Weed is a Lot of Fun

The short-term benefits of marijuana for recreational users revolve around the fact that you get high. Being high might have some negative connotations, but really it’s kind of difficult not to enjoy: you’ll feel happy, talkative, giggly and generally relaxed. It can enhance your enjoyment of many things, including music, art, movies, conversations, food and much more, and it may alter your perception of the passage of time.

Most people have heard about this stuff before, and it might be easy to brush these off and not consider them “real” benefits. However, the fact that you’ll probably enjoy being stoned is a genuine benefit, and ultimately it’s why most people use cannabis. It isn’t as important as addressing a health issue, but it’s still important.

Marijuana Impairs You in the Short-Term

Some short-term negative effects come along with the positive ones. Marijuana can make you feel nauseous or dizzy, it will probably affect your short-term memory to some extent, and it can make you feel tired or lethargic. Some people also get paranoid or anxious when they’re high, and this can even lead to a panic attack in some rarer cases.

Most of all, though, you’ll be more generally impaired when you’re high – doing things like driving or operating machinery isn’t a good idea, and you probably won’t be great at concentrating. This can also translate to a more general de-motivation if you use marijuana regularly, although this certainly isn’t the case for everybody. Likewise, if you use cannabis regularly, there’s also a roughly one in ten chance that you’ll become addicted, although it’s predominantly a psychological addiction rather than a physical one.

Marijuana Has Many Potential Medical Benefits

Medical marijuana plant

For the medical benefits of marijuana and other more “long-term” uses, there are quite a lot of different areas that scientists are investigating for potential benefits.

In many cases, it’s hard to make a definitive statement because of a general lack of evidence, due to the federal-level prohibition on cannabis which has made it difficult to study.

However, there are FDA-approved cannabis-based medications for some conditions and others have a solid evidence base that strongly suggests a benefit.

Cannabis Works Because You have an Endocannabinoid System

The endocannabinoid system (ECS) allows cannabis to have an effect on users.

It consists of two major types of cannabinoid receptors (CB1 and CB2), which are located in the brain and throughout the central and peripheral nervous systems, associated with the immune system.

CB1 and CB2 receptors can also co-exist in a variety of concentrations in the same locations.

What Type of Cannabis You Need Will Depend on Your Condition

Medical Marijuana is prescribed for a whole host of reasons across the United States. Conditions and diseases in which activation of the ECS has shown benefits are;

Multiple sclerosisCardiovascular disorders
AutismStroke (Ischemia)
Obsessive compulsive behaviorAmyotrophic lateral sclerosis
ObesityTourette’s syndrome
Parkinson’s diseaseDepression
Huntington’s diseasePanic
InsomniaPrion diseases
Alzheimer’s diseasePsychosis
Metabolic syndrome related diseases

In Brief: All Cannabinoids Have Different Benefits and Side Effects

THC comes with the heaviest side effects. CBD comes with very few, but both (and the 100+ others) have various benefits. These benefits are not always conclusive, and research is still being done. Studies suggest they broadly cover:

THC benefits:

  • Analgesic (reduces pain)
  • Antiemetic (reduces nausea and vomiting)
  • Appetite stimulant
  • Potential tumor growth inhibitor

THC side effects:

  • Difficulty concentrating
  • Lethargy
  • Paranoia
  • Heavy use (especially in youth) increases the risk of psychotic disorders
  • Long-term use can lead to addiction in around 10% of people

CBD benefits: 

  • Potential anti-tumor agent
  • Reduce seizures (especially Dravet and Lennox-Gastaut syndrome)
  • Immunosuppressive
  • Inflammatory or anti-inflammatory agent (depending on dosage)
  • Antipsychotic
  • Anti-anxiety

CBD side effects:

  • Drowsiness
  • Fatigue
  • Reduced appetite
  • Diarrhea (in rare cases)

You can learn more about the spectrum of Cannabinoids here.

Cannabis Can Help with Chronic Pain Management

Chronic pain affects many Americans, and prescription opioids have been the go-to treatment for some time, despite some obvious risks, not least of all the possibility of addiction. This has led to a lot of interest in using cannabis for chronic pain, and this has been investigated by several studies. Generally speaking, the evidence suggests a mild benefit to using cannabis for pain, but results vary quite a bit between studies and most don’t have large numbers of participants.

That said, when the National Academies of Science, Engineering and Medicine (NASEM) looked at the evidence in 2017, they concluded that adults with chronic pain treated with cannabis (or products containing cannabinoids) were more likely than those taking placebos to report a reduction in pain. While a review from 2018 found some positive effects, they noted that the benefits are small and side effects are relatively likely, and other reviews come to similar conclusions despite finding evidence of a benefit. Neuropathic pain and non-cancer related chronic pain are the main areas where cannabis could help.

Cannabis Helps Reduce Seizures for Rare Types of Epilepsy

One of the most well-known cases of cannabis – or specifically the component called cannabidiol (CBD) – having medical benefits is for a rare form of epilepsy called Dravet Syndrome. A CBD medicine called Epidiolex has been approved by the FDA for the treatment of both Dravet and Lennox-Gastaut syndrome, which are both rare seizure disorders that start in childhood.

The most well-known study on this topic compared CBD with placebo in a randomized controlled trial, assigning 120 children or young adults to either 20 mg of CBD per kg per day or placebo, as well as the standard treatment for the seizures. The patients who took CBD had their average seizures per month reduce from 12.4 to 5.9, compared to a reduction from 14.9 to 14.1 in patients taking the placebo, and they were around twice as likely to have a 50 percent reduction. One in 20 had seizures stop entirely, but they were also more likely to experience side effects like diarrhea, fatigue, fever and drowsiness.

It Reduces Self-Reported Spasticity in Multiple Sclerosis

Many different cannabis-containing medicines (including dronabinol, nabilone and nabiximols) have been studied to see if they help with multiple sclerosis (MS), along with extracts and smoked cannabis. The studies have generally found that cannabis helps with spasticity symptoms (according to the patient) but the results seem to be modest and don’t carry over when the spasticity is measured objectively. The NASEM report came to this conclusion based on their analysis of the evidence, as have many other studies.

Cannabis Reduces Nausea and Vomiting in Chemotherapy Patients

Researchers have concluded that cannabis (in particular THC, but CBD may play a role too) helps reduce the nausea and vomiting suffered as a result of chemotherapy. Based on 23 randomized controlled trials, researchers working with the Cochrane Collaboration found that cannabis-based medicines were more effective than a placebo when it comes to reducing vomiting. There weren’t many studies that compared to other medicines, but generally these showed comparable effectiveness. However, the studies tended to be small and so researchers aren’t too confident about the results.

Also, most of the studies were conducted in the 80s, which means newer antiemetic drugs (i.e. medications that stop you from vomiting) weren’t included in the comparisons and it’s largely based on older chemotherapy regimens. Despite this, the NASEM report refers to cannabinoids as “effective antiemetics” in these cases.

CBD May Help with Anxiety and More

Scientists have also found some indications that CBD in particular could help with anxiety and related conditions. For example, one small study looked at the impact of taking 600 mg of CBD on a simulated public speaking test, where 24 patients with generalized social anxiety disorder were randomized to either receive the CBD or a placebo. Results showed a reduction in anxiety and discomfort during their speech for the participants who had the CBD.

More generally, a range of evidence suggests that CBD could help with generalized anxiety disorder, social anxiety disorder, obsessive compulsive disorder, panic disorder and post traumatic stress disorder. However, a lot of this evidence only looks at the short-term effects from an acute dose, and more research is needed to make firm recommendations. It’s also worth noting that the NASEM report found that regular cannabis (i.e. CBD and THC) use increases the risk for social anxiety disorder.

What to Look For When Buying Medical Marijuana 

Buying medical marijuana means focusing on different things than when you’re buying for recreational purposes. But what’s the right type to try? This isn’t the easiest question to answer, because although fairly simple distinctions like sativa vs. indica are often used as a guide, it doesn’t actually tell you that much about the things that matter. It’s much better to look at strain-specific information when you’re considering your options.

The most important thing to think about is the amount of THC and CBD in the strains you’re considering. For conditions helped by CBD, choose a strain with roughly equal amounts of CBD and THC, or just a CBD-only product. For conditions helped by THC, look for higher-THC strains, although beware of the risk of side effects as you go higher in THC.

The typical advice (which can be useful) is that sativa strains are better for depression, anxiety and pain, and that indicas are better for things like anxiety, insomnia and inflammation. However, this is really more to do with assumptions about CBD and THC levels than the specific classification of the strain. 

Medical CBD vs Medical THC

So the real distinction you need to make is between medicinal CBD and THC, and if a combination of the two (and more) or something more focused is better for you. If you have anxiety, for instance, high-CBD strains are better for your needs, and if you have issues with pain, a higher-THC strain will be the best choice. The best way to decide what you need is by looking up the research for your condition (including the sections in this post) and at least focusing on the most important cannabinoid.

The more challenging part is working out whether you need pure CBD or a mixture of CBD and THC, for instance. Generally speaking you should try both options and see how it works for you, or see if your doctor has a recommendation based on your history. We would recommend trying CBD-only products first if that’s what you need, but for THC it’s probably better to avoid anything too pure or even super-high in THC because of potential side effects. Or at the very least, work up to a higher dose over time. Always consult your physician and seek advice from a pharmacist/dispensary on suitable strains. 

Marijuana Has Risks in the Long-Term Too

Of course, as with basically any substance, marijuana could cause problems in some cases over the long-term too. As argued above, these aren’t really “side effects” in the typical sense of the word, but they’re worth covering briefly here.

Marijuana Use Disorder

Cannabis or marijuana use disorder essentially refers to dependence on cannabis. While it doesn’t take a physical toll like dependence on most other drugs, it can have psychological withdrawal symptoms including irritability, reduced appetite, trouble sleeping, restlessness and more. 

It’s estimated that about 30 percent of people who consume cannabis have these issues to some extent, although many of these won’t have severe symptoms. You’re between four and seven times more likely to develop some type of problem if you start using cannabis before the age of 18, particularly if you do so daily.

This all happens because when you consume cannabis regularly, your brain adjusts to the increased levels of cannabinoids by reducing its own (endogenous) production and limiting its sensitivity to their effects. The symptoms are worst in the first week and generally last up to two weeks, although you can have occasional cravings for much longer than this.

Smoking Weed Might Increase Your Risk of Lung Cancer

Everyone knows that smoking tobacco increases your risk of lung cancer, but what about weed?

While it’s definitely an understandable concern, the current evidence doesn’t clearly answer the question, and some studies don’t find a link at all, while others do.

In the worst case, even the studies with stronger findings tend to find a much lower risk than that from smoking tobacco.

This might seem confusing, but the key is the amount of marijuana people smoke per day vs. the amount of tobacco. While scientists measure smokers’ intakes in “pack-years” (i.e. one pack of cigarettes – 20 – per day for a year), cannabis intake is measured in “joint-years” (one joint a day for a year). The massive difference in these two amounts – 7,300 cigarettes vs. 365 joints a year – essentially tells you why the risk for cannabis smokers is less, assuming that there is some risk.

Smoking Weed Could Cause Other Lung Problems Too

Again, with tobacco as an obvious comparison many people expect some damage to the lungs if you smoke weed. But yet again this isn’t as clear-cut as you might imagine.

Researchers have established that smoking cannabis causes injuries to the lung that make it more likely you’ll have symptoms of chronic bronchitis, but these symptoms subside if you stop smoking. As far as they can tell, smoking cannabis doesn’t cause chronic obstructive pulmonary disease (COPD), and it doesn’t seem to increase the risk of respiratory infection either.

It has been suggested that weed smoking may be a relevant factor in pneumothorax and bullous lung disease, but the evidence isn’t strong enough to demonstrate a causal link. This leaves cannabis smokers in a confusing position yet again: it’s likely that smoking weed poses some risk to your lungs, but it isn’t clear how much or whether it’s more than a non-smoker’s risk.

Cannabis Probably Increases Your Risk of Schizophrenia

One of the most famous studies on cannabis and schizophrenia looked at over 45,000 conscripts from Sweden. It found that for people who consumed cannabis on more than 50 occasions (by the age of 18), risks were six times higher than for non-users. However, the link is just an association, and finding definitive causal proof has been a challenge ever since.

On the whole, though, scientists looking at all of the data generally conclude that cannabis use does increase your risk of psychotic disorders. They can’t precisely tell the size of the relationship, and broadly the risk seems bigger in those with a pre-existing susceptibility and who use a lot of cannabis in adolescence, but it likely exists. As a best estimate in an absolute sense, the risk of schizophrenia increases from 1% for non-users to 2% for daily users. This likely stems from THC, and it’s possible that higher-CBD strains don’t carry as much of a risk, if any at all.

Smoking is the Most Risky Way to Consume Cannabis

Underpinning this discussion of the risks you might have noticed an implicit issue with smoking when it comes to the lung risks, rather than cannabis in itself. So if you want to consume cannabis but minimize your risks, it’s highly recommended that you eat your cannabis instead of smoking. Vaping is always an option too as preferable to smoking, although the science isn’t settled. And it should go without saying that mixing it with tobacco will bring with it all the risks of tobacco smoking.

This isn’t to say that vaping cannabis is completely safe – it probably does carry limited risks – but that it’s the best way to minimize your risk if you do want to partake. Likewise, if you eat cannabis, you clearly don’t have to worry about risks to your lungs, but doing so regularly could increase your risk of mental health problems over the long term.

Conclusion – Cannabis isn’t an Angel, but it isn’t “Dangerous”

Being open about the risks of cannabis isn’t ideal when we’re pretty openly fans here at CBD Oracle, but you deserve the facts before you make a decision.

Keep in mind, though, that the risks of marijuana are tiny in practice, and most of them can be avoided by making sensible decisions when it comes to how you consume. If you drink alcohol, rest assured that cannabis is much safer, and even if not you can happily have an occasional toke or brownie without having to worry. And that’s before we even get into the benefits of cannabis both medically and just in terms of the fun you can have.