Chances are you’ve heard the term THC, and you have a good sense it’s the chemical in weed that gets you high. But what do you really know about it? What exactly does THC do and how does it do it?

Table of Contents:

  • Introduction
  • THC Side effects
  • Introduction
  • General THC Side effects
  • 7 THC facts and stats
  • How does THC/marijuana affect the brain?
  • What are the physical effects of THC?
  • THC Levels – getting higher and higher.
  • Is THC addictive?
  • Cannabis use in younger people
  • Conclusion


THC is what gets you high.

But THC whose chemical name is tetrahydrocannabinol, while it is the is the ingredient which is most responsible for the intoxication and psychological effects of cannabis/marijuana represents one of many hundreds of compounds including terpenes, cannabinoids (eg CBD/cannabidiol) etc. found in the resin secretions of the cannabis plant.

While it is not produced in the body of human beings as a naturally occurring chemical it acts very much like endogenous (naturally occurring) cannabinoids such as anandamide, a neurotransmitter, and binds to receptors of the body’s endocannabinoid system. This effect on the brain allows it to alter brain function.

When we speak of THC facts we are normally referring to Delta 9 THC which is the most prevalent and psychoactive THC vs the lesser active and available Delta 8 THC.

The THC side effects may include:

  • A sense of well-being
  • Relaxation
  • Euphoria/Intoxication – i.e. being high – via THC stimulating cells in the brain to release dopamine
  • Anxiety or panic (oppose of relaxation)
  • Confusion
  • Sleepiness
  • Lowered blood pressure
  • Increased heart rate
  • Increase appetite and hunger
  • Dry mouth

THC – 7 facts and stats

Statistics about weed usage in the world is astonishing. First of all it’s smoked everywhere in the world and we know this because:

  1. How many people use marijuana worldwide? According to statistics from the United Nations almost 4% of the world populations uses cannabis and that’s well over 150 million people. (So you’re definitely not alone).
  2. In the US alone almost 100 million people have admitted to at least one time usage.
  3. As of 2007 usage in 12 to 17 year olds in US was 7% – not good. STRONGLY discourages underage use.
  4. The weed industry is over $50B in the US alone – when you include legal and illegal categories.
  5. Uruguay in 2013 was the first country in the world to fully legalize the growth and sale of cannabis.
  6. Cannabis has been around for almost 30 million years.
  7. 6000 years ago – at least. That’s how long our ancestors were smoking weed. Chilling in China, then the Middle East and onto the Greeks and Romans.

THC Weed effects on brain

How does THC/marijuana affect the brain?

Neurotransmitters are the chemicals that allow communication between nerve cells all over the body. In the brain THC by attaching to the CB1 and CB2 type cannabinoid receptors which are concentrated in certain areas of the brain, and can therefore,  affect functions and sensations including:

Short-Term Side Effects of THC

  • altered senses (for example, seeing brighter colors)
  • altered perception of time
  • mood changes
  • increased appetite
  • movement and coordination – motor effects of the brain are effected in areas such as the cerebellum and basal ganglia which are together responsible for regulating reaction time and regulate posture, balance and coordination. As such it is recommended that as marijuana may impair driving (or using heavy machinery) for approximately three to four hours.
  • difficulty with concentration, thinking and problem-solving
  • impaired memory – by interfering with information processing in the hippocampus (part of the brain responsible for forming new memories) leading to reduced ability to both learn and perform – mental and motor skills.
  • hallucinations (when taken in high doses)
  • paranoia
  • delusions (when taken in high doses)
  • psychosis (risk is highest with regular use of high potency marijuana)
  • worsening symptoms in patients with schizophrenia

Long-Term Side Effects of weed/THC on the brain

THC can be particularly damaging and incur long-term damage to younger brains as it is interfering with the processes involved in the developing brain. In fact the rate of change that is observed is much higher the younger one is and so it’s not surprising. ALl the more so because it is strongly believed that the endocannabinoid system and the receptors which make a part of that are particularly important in brain development itself.

So by using cannabis at a younger age – by impairing normal development of the brain pathways and others involved in the functions of memory, learning and thinking irreversible changes may occur (and changes that should have occurred did not).

As is often the case there is also evidence pointing to weed not leading to a decrease in IQ – when one twin smoked but the other did not.

 What are the physical effects of THC?

Respiratory problems – simply said the marijuana smoke can irritate lungs and the bronchi (tubes) and the more frequent the usage the more common and severe the symptoms can be. In fact daily cough and phlegm which are annoying are not as serious as the fact that weed smokers do have a higher frequency and risk of lung illnesses and infections. The good news is that there is no evidence suggesting that marijuana is responsible for any increased risk of lung cancer.

Increased heart rate – this can last for up to 3 hours after ingestion of the THC .

Cannabinoid Hyperemesis Syndrome – this is a serious and increasingly common set of symptoms which can include experiencing repeated cycles of severe nausea, vomiting, and dehydration.

THC Levels – getting higher and higher.

The weed our hippy grandparents did (or didn’t smoke) is not the same weed that we are smoking today in that the amount of THC in marijuana has continued to increase steadily since those groovy days. A University of Mississippi research report which analyzed marijuana preparations confiscated in the USA found a significant increase. Using data on 46,211 samples during 1993-2008 they found that the average content increased from 3.4% in 1993 to 8.8% in 2008.

But the highest concentration found was almost 30%. Today your average dispensary has many strains with over 20% THC. And as edibles have increased in popularity these have become a driver of increase adverse effects as users can consume the edibles without feeling any effects for an hour (or longer if taken on full stomach.) So together with dosage errors people consume more (trying to get high) and as such experience anxiety, paranoia, and even psychosis. The popularity of edibles also increases the chance of harmful reactions.

Is THC addictive?

Unfortunately yes it can be. That is the answer to whether marijuana is addictive and is related to the development of a substance use disorder.  This is medical illness in which although the user is suffering health and social issues in their life due to the cannabis usage they are unable to stop this damaging behavior. It is generally stated that about ten percent of the adult population using cannabis regularly can develop addiction. However more troubling is that weed usage prior to the age of 18 can increase the risk of marijuana use disorder by a factor of 4 to seven times.  People who begin using marijuana before age 18 are four to seven times more likely than adults to develop a marijuana use disorder.

People who use marijuana for a longer term, higher dosages and more frequently often report of withdrawal symptoms that make it more difficult to quit cannabis use.

Symptoms of Cannabis Withdrawal include:

  • irritability
  • sleeplessness and trouble sleeping
  • reduced appetite
  • anxiety
  • cravings for marijuana

There is good reason for serious concern over the use of marijuana for younger people, including long-term problems. Usage in the young can lead to a Decrease in IQ and Decrease in memory and cognition, especially in younger people,

A University of Montreal study published in the journal Development and Psychopathology (2016)  found that 14 year old smokers of THC containing cannabis not only did worse on cognitive tests than their non-smoking peers but also had a higher  higher school dropout rate. The same study found that those who started later (age 17) had no such correlations.

Another study from New Zealand showed that heavy usage of cannabis starting in the early teens led causing people who started marijuana use disorder lost 8 IQ points on average by age 38 and this loss was not fully recoverable even when they stopped smoking as adults. Conversely those who began smoking even as adults did not demonstrate significant decline in IQ).


  • THC is a chemical that is similar to naturally occurring cannabinoids in the bodies of vertebrates and which stimulates the endocannabinoid system.  It is derived from  the dried leaves, flowers, stems, and seeds from the Cannabis sativa or Cannabis indica plant.
  • THC affects many parts of the mind and body
  • THC has one of the safest profiles of any drug and but can still cause significant and uncomfortable side-effects
  • Ingestion can be via smoking, eating, drinking, or inhaling it using vapes.
  • THC levels have been increasing for decades and are found even more concentrated in certain formulations (e.g. dabs and concentrates) and also can be easily over consumed via edibles.
  • THC over activates certain brain cell receptors, resulting in effects such as:
    • altered perceptions including psychosis
    • changes in mood
    • euphoria
    • impaired body coordination movement
    • difficulty with thinking and problem-solving
    • impaired memory and learning
  • THC is addictive in predisposed individuals and the risk is much higher when used prior to age 18
  • People under 18 should completely abstain from cannabis use

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