EducationWhat is THC and how does it work in the body

What is THC and how does it work in the body

11 min read

Kerry Charron

What is THC and how does it work in the body


THC, short for tetrahydrocannabinol, is one of the 113 cannabinoids that have been isolated from the cannabis sativa L. genus (which includes both cannabis and hemp varieties). It is primarily known for its psychoactive and intoxicating effects, and so it is most often associated with recreational cannabis.

Over the course of the last 50 years or so, extensive research has uncovered a captivating assortment of potential therapeutic benefits linked to THC. And thanks to the current proverbial tidal wave of both recreational and medical cannabis legalisation sweeping the globe, the rate at which this research is being conducted is increasing at an almost exponential rate.

The discoveries that have been made so far indicate that THC possesses a surprisingly diverse range of medicinal properties, paving the way for its utilization in various treatment approaches. From alleviating pain to safeguarding neurological functions, the therapeutic capacity of THC continues to mesmerize scholars and stimulate ongoing investigations into its applications.

But it's not only modern medicine that has been abuzz with the potential of THC, or medical cannabis in more general terms. The therapeutic potential of cannabis cultivars has been documented as far back as almost five millennia ago (2800 BC), when the Chinese emperor Shen Nung, who is widely regarded as the 'father of Chinese medicine', mentioned its application for treating a range of ailments in his famous treatise on pharmaceuticals. From there we see it being mentioned in the works of numerous civilizations, from the Egyptians to the Persians, Romans to the Greeks, and even in ancient Indian and Sri Lankan wellness-focused texts such as the Ayurveda.

So how does this remarkable compound interact with the human body?

That is the question that we will be breaking down in today's article. We will be taking a detailed look at THC and how it interacts with the endocannabinoid system to produce its therapeutic effects, while trying to keep the lingo as 'user-friendly' as possible. So, without any more delay, let's dive in…

What is THC?

In the simplest of terms, THC is a phytocannabinoid (a cannabinoid produced by plants) that is found in high concentrations in certain cannabis strains, and much lower levels in hemp. When administered, THC binds to the cannabinoid receptors in our bodies (CB1 and CB2) which are one part of something called the endocannabinoid system (ECS).

This system is made up of three main components:

  • The CB1 and CB2 receptors
  • Endocannabinoids, which are molecules that our bodies naturally produce that act as the ‘keys’ that unlock the cannabinoid receptors, triggering the physiological responses
  • Enzymes, which help metabolise and breakdown cannabinoids once their function has been completed

The ECS is the body’s master regulatory system and the largest neurotransmitter network. It has been shown play a role in the regulation of homeostasis (maintenance of a stable internal environment despite changes in the external environment) as well as various other physiological processes, such as pain sensation, metabolism, immune responses, sexual function, and memory.

THC is able to interact with the ECS receptors due to the fact that its chemical structure is remarkably similar to one of the cannabinoids produced by our own bodies, anandamide (AEA). This similarity allows THC to mimic the behavior of natural cannabinoids and activate CB1 and CB2 receptors.

THC has been shown to have a stronger affinity to the CB1 receptor sites than CB2. CB1 receptors are mainly found in the brain and central nervous system, where they are associated with a variety of physiological responses such as pain relief, memory, motor control, appetite, and mood regulation. Activation of the CB1 receptors by THC produces a wide range of effects including euphoria, relaxation, altered perception, pain relief, inflammation reduction, and increased appetite.

The science behind potential therapeutic benefits of THC

Before we dip our toes into the potential therapeutic benefits of THC, we must first point out that even though there are a lot of promising research papers and clinical trials that have already been conducted, much more work still needs to be done in order to conclusively establish these effects. It is also important to point out that THC, and medical cannabis as a whole, should never be regarded as a replacement for conventional medications, but rather as an additional treatment option that can be explored in certain cases.

With that said, THC looks to be a great complementary option for a surprisingly wide range of medical conditions, with research indicating that it is a potential treatment for pain, inflammation, neurological disorders, glaucoma, nausea, mental health issues, and even muscle spasticity.

THC for pain

Pain is usually split into three main categories – acute, chronic, and neuropathic.

  • Acute pain is the most common type of pain, including injuries like sprains or strains, or post-operative issues. It typically lasts for days or weeks before gradually subsiding, during which the body heals naturally.
  • Chronic pain is a persistent type of pain that lasts for months or even years and is often linked to conditions like arthritis, fibromyalgia, back issues, and migraines. Managing everyday life becomes challenging due to ongoing discomfort.
  • Neuropathic pain, also known as nerve pain, occurs when the nervous system is damaged or irritated due to various factors such as injuries, infections, or medical conditions. This type of pain is characterized by shooting sensations, numbness, tingling, and a burning or electric shock-like feeling. It is crucial to understand the underlying causes and seek appropriate medical treatment in order to effectively manage and find relief from neuropathic pain.

When it comes to acute pain, THC has shown the potential to offer rapid relief without the need for any additional medications.

One clinical medical review, which looked at a range of differing back pain related issues from a total of 110 patients, found that medical cannabis application proved to be extremely efficient, while heavily reducing the need for opioid medications. This is an especially important discovery given the current opioid epidemic in the UK and US.

For chronic pain, there are a range of studies we can look at, but this systematic review does so for us. Focusing on twenty-five separate studies, it found that

“Cannabis products with high THC-to-CBD ratios and sublingual, extracted cannabis products with comparable THC-to-CBD ratios may be associated with short-term improvements in chronic pain”

And for nerve pain, the results also look promising. In a randomized controlled trial from 2010, titled "Smoked cannabis for chronic neuropathic pain", it was discovered that a single inhalation of 25 mg of 9.4% tetrahydrocannabinol herbal cannabis, three times daily for five days, effectively alleviated pain intensity, enhanced sleep quality, and exhibited safe and high tolerability.

THC for glaucoma

Glaucoma is a complex disease that is not typically caused by a single issue, but rather a combination of conditions that can lead to vision impairment or even complete blindness. It ranks among the top causes of blindness in adults and can be classified into three main groups:

  1. Primary Glaucoma: There are two primary types of glaucoma - primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG). These are the most common forms.
  2. Secondary Glaucoma: This type of glaucoma occurs as a result of other medical conditions or trauma.
  3. Developmental Glaucoma: Glaucoma that affects children and infants. It is an extremely rare form, with only around 5 in 100,000 children being affected.

THC application may help reduce the severity of glaucoma through two separate mechanisms.

Firstly, THC can reduce intraocular pressure (IOP) in the eye due to its ability to dilate blood vessels and decrease fluid production, reducing inflammation in the eyes which can help slow down the progression of glaucoma.

Secondly, the cannabinoids that interact specifically with the CB1 receptor, such as THC, have shown promising therapeutic potential for addressing corneal surface damage and alleviating associated pain. By targeting the CB1 receptor, these cannabinoids may help modulate the signaling pathways involved in corneal healing and provide relief from discomfort, offering a potential avenue for the development of novel treatments in this field.

THC for the reduction of nausea and vomiting

One of the earliest medical applications of cannabis was in alleviating nausea and vomiting, particularly in cancer patients undergoing chemotherapy. In 1986, the US Food and Drug Administration (FDA) granted approval for a synthetic form of THC to be prescribed for patients undergoing chemotherapy to help address the heavy nausea that often goes hand in hand with the treatment.

And the science has only grown since then. One of the more recent clinical trials, titled "Regulation of nausea and vomiting by cannabinoids" found that activating the CB1 receptor had a marked affec ton the reduction of nausea and vomiting when compared to a placebo group. The results showed that THC had a clear antiemetic effect, helping reduce the severity of symptoms in both healthy individuals and cancer patients undergoing chemotherapy.

THC for the treatment of muscle spasticity

Muscle spasticity is a symptom related to a range of different medical conditions, including multiple sclerosis (MS), spinal cord injuries, and cerebral palsy. It is characterised by stiff or rigid muscles that are difficult to control, causing issues with coordination and balance. The condition can also be very painful as the body struggles to move in the way it wants to.

One large scale study that focused on MS patients found that throughout the 15 week trial, participants that were given oral THC extract showed

"there was evidence of improvement in walking time for ambulatory patients and in patient perceptions of spasticity, muscle spasms, pain, and sleep" and that "There was evidence of a treatment effect on patient-reported spasticity and pain (p=0.003), with improvement in spasticity reported in 61%"

Are there any risks or side effects to THC administration?

Although THC is an effective therapeutic agent, it does come with some potential risks and side effects, which need to be considered when exploring medical cannabis as a treatment option.

The most common side effects associated with the consumption of THC are dizziness, drowsiness, dry mouth, and red eyes. It can also lead to anxiety or paranoia when taken in high doses.

It is important to note that THC does have the potential for abuse and can produce a dependency in some individuals. This risk should be considered when determining whether medical cannabis is an appropriate treatment option.

With all of that said, it should be obvious that it is essential to consult a doctor that is qualified to prescribe medical cannabis before beginning any form of THC therapy.


Medical cannabis became a legal reality in the UK in November 2018, and it has gained traction as an effective treatment for many medical conditions, including glaucoma and muscle spasticity.

THC, through its interactions with the body's endocannabinoid system (ECS), has been shown to offer a range of therapeutic benefits and can be a great complement to conventional medications and therapy options.

Releaf understands that finding a doctor who is registered to prescribe medical cannabis can be difficult. That's why we offer online consultations with our specialist doctors, as well as a unique medical cannabis card for extra protection and access to the treatment you need. If you're interested in learning more about our services or getting access to medical cannabis treatment, get in touch and one of our team members will be happy to help.

It is important to seek medical advice before starting any new treatments. The patient advisors at Releaf are available to provide expert advice and support. Alternatively, click here to book a consultation with one of our specialist doctors.

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Kerry, with experience as a medicinal cannabis cultivation technician and expertise in business licensing applications, is passionate about developing educational content and advocating for better access to medical cannabis worldwide.

Our articles are written by experts and reviewed by medical professionals or compliance specialists. Adhering to stringent sourcing guidelines, we reference peer-reviewed studies and scholarly research. View our editorial policy.

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Editorial Team