The further you venture into the world of medical cannabis, the more confusing the differences between cannabidiol (CBD) and tetrahydrocannabinol (THC) can become. They are often mentioned in the same breath and come from the same plant.
Despite their similarities, CBD and THC are quite different in their effects. As a result, it’s important to understand the distinctions and why you may be prescribed one instead of the other or a specific blend of both.
Let’s walk through the differences between CBD and THC, how each affects your body and how Australia regulates them both.
The Difference Between CBD & THC
Both CBD and THC are natural compounds found in the cannabis plant and both work with your endocannabinoid system to produce effects in the body and mind. The main difference between THC and CBD lies in the way these compounds bind to CB1 and CB2 cannabinoid receptors to cause an effect.
For example, one of the most well-known differences between THC and CBD is that THC is psychotropic and may cause intoxication (a so-called "high") while CBD is not psychotropic. CBD is also thought to interact with other receptors in your body & may counteract some of the negative side effects of THC.
Both CBD and THC are derived from the Cannabis plant. However, CBD is typically derived from a hemp-type plant lower in THC, while THC is derived from a plant which contains a higher level of THC alongside CBD.
Both THC & CBD are legally available via script for medical use in Australia. Legally, doctors can prescribe both THC, CBD or blended prescription products. CBD has been recently down-scheduled to a Schedule 3 (pharmacist only medicine), but it isn’t yet available through over-the-counter purchases. THC remains strictly Schedule 8 (controlled drug).
Finally, both CBD and THC can be ingested through topicals, tinctures and vaping, to name a few methods.
What Is CBD?
CBD is extracted for medical use in oils, capsules and other products that are commonly prescribed for relief from symptoms like pain, anxiety and insomnia. Over the last decade, it has gained traction for its calming effects, especially in countries like the United States and Canada where CBD is available over-the-counter in a wide range of formats.
Here in Australia, CBD is typically prescribed through the Therapeutic Goods Administration’s (TGA) Special Access Scheme. An increasing number of doctors are prescribing CBD to patients for relief from symptoms and conditions like pain, anxiety and sleep disorders.
What Is THC?
Tetrahydrocannabinol (THC) is another cannabinoid and, together with CBD, makes up the majority of the cannabinoids in most cannabis strains. It was first discovered in 1964 and has become famous for producing the “high” marijuana is known for – but it has a lot of potential therapeutic benefits beyond this psychotropic effect.
When consumed, THC interacts with the cannabinoid receptors in your brain and body; the exact pathway depends on your method of ingesting the THC (vaping or orally). THC is often prescribed to treat chronic pain, insomnia, nausea and lack of appetite, muscle spasticity and anxiety.
In a review published in the Australian Journal of General Practice, cannabis containing THC was described as “a relatively safe drug, and it is not associated with fatal overdoses.” It is available with a prescription through the TGA’s Special Access Scheme (SAS).
CBD vs THC: Chemical Structure
There are more chemical similarities between CBD and THC than there are differences. Both are similar to your body’s own endocannabinoids, which allows them to interact with your cannabinoid receptors to release neurotransmitters in your brain.
They also have the same molecular structure of 21 carbon atoms, 30 hydrogen atoms, and two oxygen atoms; however, the atoms are arranged differently.
This seemingly small difference has a major effect on the body. It is essentially responsible for changing the way each compound interacts with the endocannabinoid system’s receptors to produce an effect like the "high" associated with THC.
How CBD and THC Affect the Body
Before we consider how CBD and THC affect the body, it’s important to understand the role your endocannabinoid system plays.
The endocannabinoid system, first discovered in 1992, refers to a network of receptors in your body known as CB1 and CB2. CB1 receptors are mostly found in the central nervous system, while CB2 receptors are mostly found in your peripheral nervous system and immune cells. Endocannabinoids bind to these receptors to send signals to your body, which affect various tissues and bodily functions.
CBD and THC are two of the more than 100 cannabinoids in the cannabis plant. These ‘phytocannabinoids’ are similar to your body’s own endocannabinoids, making them effective at binding to receptors to prompt certain changes.
However, THC & CBD interact with your endocannabinoid system in different ways. For example, THC binds to CB1 receptors to produce a number of effects, including a psychotropic effect commonly known as a "high". Meanwhile, CBD predominantly binds to CB2 receptors and acts as a modulator, producing different therapeutic effects with no associated high.
When CBD and THC are combined, patients can benefit from the entourage effect, whereby combined compounds have a different effect on the endocannabinoid system than either would alone. For example, there is some evidence that suggests the two combined can offer greater pain relief than either compound alone.
Exactly how CBD, THC or a combination of the two affects your body will depend on your own physiology, with things like metabolism playing a role. Lifestyle factors, other medications and the symptoms you hope to treat will also contribute. This is why it is important to speak to a doctor who is well-versed in cannabis as medicine and to take a ‘slow and low’ approach to your dosage.
Medical Benefits of THC & CBD
The discovery of the endocannabinoid system is still recent and there is much more to explore. But what we do know is that it is essential to our well-being, with research suggesting it plays a role in cardiovascular function, digestive function, immune response, inflammation, memory and more.
Given THC and CBD’s similarities to the endocannabinoids found in the body, there is potential they will have a medical benefit in each of these important functions. Here is just a little of what we know so far.
Benefits of THC
One of the more well-established medical benefits of THC is that it can help reduce nausea or stimulate appetite. In the United States, the Food and Drug Administration (FDA) has approved two synthetic formulations of THC to treat chemotherapy-induced nausea and vomiting and to stimulate appetite in people with AIDS or anorexia.
Here in Australia, chronic pain is the most common reason people are prescribed medical cannabis. When it comes to THC, it is thought that THC can help patients mentally cope with pain rather than reducing the pain itself.
Similarly, there are studies that show THC can help alleviate anxiety in some patients and can have a positive effect on sleep, depending on the specifics of a patient’s insomnia.
Benefits of CBD
CBD has been shown to be an allosteric modulator, helping to regulate how much the body listens to particular signals, including pain. These two effects may explain why CBD can help patients find relief from chronic pain.
In countries where CBD is legal or regulated, it is often prescribed to individuals who are struggling with seizures, inflammation, inflammatory bowel disease or migraine. In Australia, the TGA has approved a prescription medication containing CBD that’s used to treat rare forms of childhood epilepsy.
Chronic pain, anxiety and cancer pain are the three most commonly cited indications for prescriptions, according to data from the TGA.
When it comes to risk factors and potential side effects, CBD and THC are quite different. In general, CBD is a safer option for all types of patients, though both are generally considered safe for patients who are following a protocol prescribed by their doctor.
THC Risk Factors
THC is contraindicated in patients with a history of schizophrenia and psychosis. Currently the scientific literature shows there is a correlational link between the administration of cannabis and psychosis.
Like most medicines, side effects can be difficult to anticipate as so much depends on the patient’s genetic makeup, lifestyle, mental state and metabolism.
Although usually mild, THC can cause symptoms like disorientation, dry mouth, vertigo, memory impairment, intoxication, and dizziness. While overconsumption is incredibly rare, it can increase the chances of a patient experiencing side effects like dizziness or anxiety.
Patients who use cannabis regularly may find that, eventually, it does not provide the same relief it once did as tolerance increases. In these cases, a T-break, where a patient takes a break from using cannabis to reset their sensitivity, could help.
CBD Risk Factors
There are fewer adverse effects associated with CBD, and it is generally well tolerated, even in high doses. Titration is still recommended when commencing CBD treatment, following the start low and go slow ethos to reduce the chances of potential interactions with your other medications.
One of the most common side effects of CBD treatment is diarrhoea, while in rare circumstances CBD may cause liver damage, which is usually associated with very high doses or interactions with other medications that are metabolised in your liver.
CBD vs THC: Legality in Australia
On the 24th of February, 2016, the Australian Government passed legislation that allowed patients with specific conditions to access medicinal cannabis products with a prescription. Since then, there have been several changes that have changed the way the TGA regulates CBD and THC.
Most notably, in December 2020, the TGA decided to down-schedule CBD to a pharmacist-only medicine. This meant CBD oil should be legal for purchase over the counter at your local chemist.
This is not yet the reality because of one crucial requirement on the pharmaceutical company’s side. The Australian Register of Therapeutic Goods (ARTG) requires anyone selling medicine in Australia to submit sufficient data to certify a product’s safety, efficacy and overall quality.
Generating this research is financially prohibitive for most pharmaceutical companies, and even larger companies have yet to justify the cost vs. profit. This is why Aussies are not yet able to purchase CBD over the counter, despite it being legal.
In 2021, the Government changed the way the application process for medical cannabis products worked, allowing doctors to prescribe medicinal cannabis without needing separate approvals for individual patients and to create generic prescriptions rather than brand specific.
Although the progress we’ve seen so far has been promising, there are still areas where Australia lags behind. Because of this, medical marijuana patients in Australia need to be aware of things like employment laws and the rules around cannabis and driving.
Finding The Right Product For You
Understanding the many terms associated with medicinal cannabis can be helpful for patients, and THC and CBD are two you’ll encounter time and time again.
Although they are similar in some ways, these cannabinoids have different effects on the body and, like many medicines, different effects on different individuals. Talk to your doctor or book an appointment at a medical cannabis clinic if you’d like to discuss their potential therapeutic role in your own health journey.