Marijuana is a mixture of dried flowers from a plant called Cannabis sativa that contains around 420 chemical compounds, around 60 of which are called cannabinoids. The most well-studied cannabinoid is called delta-9-tetrahydrocannabinol, or THC.
When you smoke or ingest marijuana, THC enters your bloodstream from your lungs and is subsequently distributed throughout your body. Cannabinoids such as THC have a variety of physiological effects, including palpitations, dizziness, and coughing, in addition to its actions on your brain, such as euphoria, a sense of relaxation, and heightened sensory perception.
If you’re reading this, chances are that you have experienced some of these effects before. Every individual will have a different set of reactions to marijuana culminating in a unique experience. Ultimately, though, the underlying biological mechanisms driving your subjective experience are shared between people. Our goal is to translate the science behind marijuana’s effects, so that you can better understand how your experience occurs at the molecular level!
Understanding Effects on the Body
The precise timing of marijuana’s bodily and mind-altering effects will vary depending on how you use, and how much. When you smoke marijuana, you likely experience a ‘high’ sensation that can occur as soon as 10 minutes after ingestion, and which can last anywhere from 45 minutes to 3 hours after smoking. In contrast, when you consume marijuana in an edible form, the drug must first pass through your digestive system before it can enter the bloodstream and exert its effects. This leads to a slower onset of effects (usually taking 30-60 minutes), duration of effects (usually lasting 3 to 8 hours), and variety of effect intensity, as it can sometimes be difficult to tell exactly how much marijuana you’re consuming in an edible format.
Effects include, but are not limited to:
- Feeling of increased pressure inside the head
- Increased heart rate
- Dryness in the eyes and mouth
- Redness in the eyes
- Sensitivity to light
How can cannabis be responsible for all of these reactions? Your body possess a molecular signaling system called the endogenous cannabinoid system, and consists of self-produced cannabinoid compounds, as well as corresponding cannabinoid receptor proteins located on the surfaces of a various cell types and organs throughout your body. The cannabinoids that we naturally produce bind to cannabinoid receptors in a lock and key fashion to turn these receptors on. Activation of cannabinoid receptors trigger a cascade of intracellular effects.
That’s not all. There are actually two types of cannabinoid receptors: CB1 and CB2. CB1 receptors are found primarily in your brain, while CB2 receptors are found throughout the body which leads to the wide-ranging effects of cannabinoids in a variety of bodily processes, from inflammation, to blood flow, to appetite regulation. Cannabinoids in marijuana, namely THC, are very similar in chemical structure to the cannabinoids that your body produces, which allows them to bind to and activate CB1 and CB2 receptors. All this to say that, while marijuana’s wide constellation of symptoms may seem totally unrelated, they are all linked by shared neurobiological mechanisms!
Nervous System Effects
The mechanisms by which marijuana can alter mood and perceptions is fascinating. At a molecular level, THC’s chemical structure bears resemblance to a naturally produced compound in the brain known as anandamide, or AEA (Scherma, Nature, 2018). This structural likeness allows THC to bind to the CB1 receptors in your brain that anandamide would normally bind to and in order to produce its rewarding, mind-altering effects. In fact, “ananda” is derived from the Sanskrit word for “internal bliss”!
CB1 receptors are found in higher clusters in specific regions of the brain. When cannabinoids bind to these receptors, they inhibit the release of certain neurotransmitters that your body typically produces–including acetylcholine, dopamine, serotonin, and glutamate—to regulate a host of functions within your nervous system. Specific areas of the brain which contain CB1 receptors include:
- The basal ganglia: this area of the brain is responsible for movement and also houses your “reward system”, which explains why marijuana may lead to a sensation of slowness, euphoria, and an increased response to pleasurable activities such as eating and sex. When you use, THC acts like anandamide, and stimulates neurons in your reward system to release more dopamine than what your brain normally accustomed to.
- The prefrontal cortex: also known as the PFC, this area is responsible for higher-order brain functions such as inhibition and executive processing, which explains why you may experience disinhibition and altered decision-making abilities while high.
- The cerebellum: the cerebellum is responsible for coordinating smooth body movements. Feeling unbalanced, uncoordinated, or otherwise off-kilter when you’re under the influence is in part through marijuana’s actions on the cerebellum.
- The hippocampus: this brain territory is the core of learning and memory, which explains why marijuana may lead to short-memory impairment.
Many people experience pleasant cognitive effects, such as:
- Increased relaxation
- Altered perceptions
- Feeling as though time is slowed down
- Colors appearing brighter
- Enhanced appreciation of visual details
- Enhanced perception of noises and sounds
- Enhanced appreciation of music
- Enhanced taste
However, some people may experience more negative cognitive effects with marijuana. This is especially true if you are dependent, or if the marijuana you consume is of unexpectedly high potency. Factors like inexperience will put you are higher risk for consuming too much and precipitating a bad trip. These potential negative cognitive effects include:
- Increased appetite
- Nausea/Stomach Upset
- Lack of motivation
- Attention and processing speed deficits
- Memory impairments
- Impaired movement and movement coordination
Marijuana’s effects on your nervous system are therefore wide-ranging and vary dramatically between users. After all, THC isn’t the only neurotransmitter at play. Adding to this, your subjective experience is inevitably influenced by host of other factors, including your physical environment and your pre-existing mood state.
Issues from Chronic Marijuana Use
Short Term Effects
Acute intoxication with marijuana affects multiple dimensions of thought, body, and mind. It can slow reaction time and impair motor coordination, attention, concentration, short term memory, and your ability to act in risky situations. These effects may interfere with your ability to complete complex tasks that require high levels of attention (Boggs, J Psychopharmacol, 2018). While they are temporary, these effects can often last 12-24 hours longer than the sensation of euphoria you initially experience, due to the buildup of the drug in your body’s fatty tissues.
Acute intoxication with marijuana increases the sympathetic activity in your nervous system, which is oftentimes referred to as your “fight or flight” drive. This can cause your heart to race and can even sometimes cause chest pain that may feel like a heart attack. Although there have been case reports of heart attacks in young people with no identifiable causal factors other than recent marijuana use this appears to be a rare phenomenon (Velasquez, J Am Coll Cardiology, 2020). From what we know so far, there does not currently appear to be a direct significant association between marijuana use and cardiovascular disease.
In rare situations, ingesting large amounts of marijuana can even lead to a break with reality. Psychosis is the technical medical term that is used to describe this dangerous mental state, which entails hallucinations, delusional ideas, and a sometimes loss of personal identity. Unlike chronic psychotic disorders like schizophrenia, however, this unpleasant and extreme reaction to marijuana is temporary. Recent research has shown that smoking high-potency marijuana on a daily basis may increase your chances of developing psychosis by almost 5 times compared to people who have never used marijuana (Di Forti, The Lancet, 2019). The interaction between marijuana use and psychiatric disorders is undergoing ongoing investigation, and the nuances of this relationship require further study before we can claim to fully understand it.
Effects of Continued Use
When you smoke a lot or very frequently, your body eventually becomes used to having marijuana in your system around the clock. Your body’s natural reaction to this is to down-regulate the number of CB1 receptors in your brain in a process called “desensitization,” as your CB1 receptors adjust to increased levels of stimulation (Bonnet, Subst Abuse Rehabil, 2017). When you discontinue using marijuana, these receptors are left with only your body’s natural cannabinoids and a smaller number of receptors to act through. This receptor scarcity causes lower amounts of cannabinoid signaling in your body, and triggers short-term symptoms of withdrawal such as:
- Difficulty with sleep
- Decreased appetite
- Abdominal pain
- Shakiness or tremors
- Fever or chills
Although these withdrawal symptoms can be very uncomfortable, it is important to understand that they are not life-threatening and will eventually go away on their own. In our entire section devoted to Marijuana Withdrawal, we detail what you can reasonably expect during withdrawal, including the most common symptoms, timeline and strategies to combat them.
You may be wondering whether long term marijuana use has long-term or permanent effects on your brain, and if so, you’re not the only one–as we speak, there is a ton of ongoing research investigating this very question. We’ve condensed this huge body of ongoing scientific study into the big highlights on the long-term impact marijuana may have on different organ systems.
- In one analysis of multiple studies on young adults and adolescents, researchers found that while frequent marijuana use does impact multiple brain functions (such as your ability to learn new material, process information, and remember things) in the short term, most of these impairments were barely detectable after 72 hours of abstinence from marijuana (Scott, JAMA Psychiatry, 2018).
- Once people reach adulthood, however, cumulative exposure to marijuana is associated with poorer performance in some aspects of brain function compared to others, especially if marijuana use is ongoing (Schulte, Clin Psychol Rev, 2014; Auer, JAMA Intern Med, 2016).
- An analysis of multiple studies of brain structure and function in adults who use marijuana found consistent evidence of reduced volume in the specific brain region of the hippocampus, but not in the brain overall. Functional neuroimaging studies found that adult marijuana users have decreased brain activity in specific regions (the anterior cingulate cortex and right dorsolateral prefrontal cortex, to be specific), but have functional connectivity in other brain regions. Abnormalities in neuronal activity were seen even when performance on cognitive tasks were normal, suggesting that marijuana users may engage different parts of their brain to accomplish mental tasks than those who don’t use marijuana (Nader, A J Drug Alcohol Abuse, 2018). Though it’s difficult to say how relevant these findings may be for the actual impact marijuana has on your brain’s ability to function, there does seem to be some degree of impact that is not yet fully understood.
- When you smoke cannabis, you aren’t just inhaling weed—you’re also inhaling respiratory irritants and cancer-promoting molecules, many of which are also found in tobacco smoke. Cannabis fumes therefore cause transient lung damage and airway irritation, which manifests as cough, wheezing, and chest tightness (Gates, Respirology, 2014).
- So far, however, there are no clear associations between chronic use and long-term impairments in lung functions or lung diseases, including obstructive lung disease, lung cancer, or asthma (Kempker, Ann Am Thorac Soc, 2015).
- While acute marijuana intoxication can cause transient chest pain, there does not appear to be any obvious long-term increase in risk of heart attacks or stroke (Ravi, Ann Intern Med, 2018).
- A growing number of anecdotal medical reports are drawing a potential connection between marijuana use and development of an abnormal heart rhythm called atrial fibrillation. In atrial fibrillation, abnormal electrical signals in the heart create abnormal heart rhythms. People may feel their heart skipping beats, fluttering, racing, or nothing at all. While atrial fibrillation is associated with a number of important potential health consequences, the absolute risk of marijuana associated with atrial fibrillation appears to be small (Korantzopoulos, Int J Clin Pract, 2008).
- Cannabinoid hyperemesis syndrome (CHS), also known as cyclic vomiting syndrome (CVS), is a rare but serious condition that can develop suddenly in people who are daily marijuana users or in people who have a history of prolonged marijuana use. When you have CHS, you experience episodes of intractable nausea and vomiting, oftentimes to the point that you are unable to keep down food or water (Sorensen, J Med Toxicol, 2017). One of the hallmarks of CHS is relief of nausea with hot showers or baths, and many people find that this is the only way to improve their symptoms. The exact pathophysiology of CHS is unknown, but as marijuana use becomes more common, doctors and healthcare providers increasingly have this marijuana-related complication on their radar, as should you. People with CHS may require hospitalization in order to maintain hydration while their nausea and vomiting persist. While anti-emetic or anti-nausea medications would make sense as treatments for CHS, the hard reality is that they aren’t solving the underlying issue. At the end of the day, the only proven way to treat CHS is to stop using marijuana, and permanent cessation of marijuana use leads to the only assured cure (Richards, J Emerg Med, 2018).
- Additionally, daily marijuana use has been shown to worsen the progression of chronic viral hepatitis C infection, which is an important consideration if you know that you have this infection (Hézode, Hepatology, 2005).
- Active marijuana use has been found to be associated with decreased sperm count through hormonal dysregulations, consequences of which may include decreased fertility (du Plessis, J Assist Reprod Genet, 2015).
- Long-term marijuana users have been shown to have approximately 20% lower levels of a hormone called prolactin in their bloodstream. Prolactin normally functions to promote production of breast milk following childbirth (Ranganathan, Psychopharmacology, 2008). Marijuana may therefore interfere with ability to produce milk in breastfeeding mothers (Barnett, Addict Behav, 2012).
- Additionally, marijuana is able to freely cross the placenta during pregnancy, making use of the drug during pregnancy problematic for both women and their unborn children. Babies exposed to marijuana while in the womb are at risk of low birth weights, and are more likely to need placement in the neonatal intensive care unit (Metz, A J Obstet Gynecol, 2015). Overall, if you’re pregnant and deciding whether it’s safe for you and your baby to use marijuana, experts would agree that the drug should be avoided.
- Marijuana use is associated with inflammation of your oral mucosa, increased risk of periodontal disease, and oral candidiasis (fungal overgrowth in your mouth) (Cho, Aust Dent J, 2005).
Time to Recover from Effects
Acute intoxication from marijuana can have a variable length of action, but the sensation of euphoria or ‘high’ it induces can occur as soon as 10 minutes after intake and, depending on how much you use, may last anywhere from 45 minutes to 3 hours. In contrast, when you consume marijuana in an edible form, the drug must first pass through your digestive system before it can enter the bloodstream and exert its effects. This leads to a slower onset of effects, usually between 30-60 minutes, as well as longer duration of effects lasting anywhere from 3 to 8 hours.
While the immediate effects of marijuana typically subside within hours, it’s entirely possible that it may take days in order to feel entirely back to normal. If you’ve developed dependence to the drug, you are almost certain to experience some degree of withdrawal that sets in 24 to 72 hours after cessation of use. Thus, recovering from marijuana can be hugely frustrating: right as you overcome its acute effects, you feel other symptoms starting to kick in. Withdrawal symptoms usually reach peak intensity over the first week, and largely resolve after 1-2 weeks, although symptoms can certainly persist for weeks to months after quitting (Bonnet, Drug Alcohol Depend, 2014). Sleep disturbances, which are hallmark of marijuana withdrawal, may last up to several weeks. While these symptoms are self-limited, and will eventually go away on their own, that doesn’t mean they’re tough to deal with. Jump to our section on Marijuana Withdrawal to read more about the specific withdrawal symptoms.
Finally, it is unclear how long the physiologic effects from long-term marijuana use, such as Cannabis Hyperemesis Syndrome or decreased sperm count, may last after quitting marijuana. Active research is ongoing that will hopefully determine the impact that long-term marijuana use has on the body.