CBD vs THC – what’s the difference?

Marie Law Alphabiolabs

By Marie Law, Head of Toxicology at AlphaBiolabs
Last reviewed: 28/02/2023

Cannabidiol (CBD) and tetrahydrocannabinol (THC) are chemical compounds found in cannabis and derived from the Cannabis sativa plant.

While both are classed as cannabinoids, there are some fundamental differences between the two.

Here, we explore CBD and THC, how the two are different, and the side effects of using each substance.

Table of contents
  • What is THC?
  • What is CBD?
  • What are the differences in chemical composition between THC and CBD?
  • What are the medical benefits of CBD?
  • What are the medical benefits of THC?
  • What are the side effects of CBD and THC?
  • Is THC legal in the UK?
  • Is CBD legal in the UK?
  • Where can I buy a drug test?

What is THC?

Tetrahydrocannabinol (THC) is a chemical compound and the main psychoactive ingredient found in cannabis.

This means that THC is responsible for the ‘high’ that people experience when using cannabis.

It is most commonly ingested by smoking cannabis. However, some people also vape it using electronic cigarettes/atomisers, or infuse it into food or drinks including biscuits, cakes, and tea.

Food and drinks that contain cannabis are known as ‘edibles’ or ‘cannabis edibles’.

What is CBD?

Cannabidiol (CBD), is a chemical found in cannabis. Unlike cannabis however, CBD causes few if any psychoactive effects.

This is because CBD only contains small amounts of tetrahydrocannabinol (THC) – the psychoactive ingredient in cannabis.

It is typically sold in select shops or online in the form of CBD oil but can also be found as an oil-based capsule or in liquid form.

In the UK, CBD is heavily regulated and must not contain any more than 0.2% THC when sold over the counter.

What are the differences in chemical composition between THC and CBD?

Although both CBD and THC are cannabinoids derived from the Cannabis sativa plant, each has a different composition.

Each shares the same molecular structure but the atoms within them are arranged differently. This means that CBD and THC have different effects on the body.

For example, THC is the main psychoactive ingredient found in cannabis, and is responsible for the physical and psychological side effects people experience when they take cannabis.

When a person uses cannabis, THC binds to specific receptors in the brain. In many people, this produces a sense of euphoria.

In contrast, CBD binds very weakly if at all to the brain’s receptors, meaning that it produces few if any psychoactive effects.

What are the medical benefits of CBD?

Although not common, when used in medical settings, CBD is sometimes prescribed to treat certain health conditions including epilepsy, multiple sclerosis (MS), and nausea and vomiting experienced by adults undergoing chemotherapy.

CBD is only usually prescribed where other treatments and medications have failed or are unsuitable.

Clinical studies are also being undertaken to determine whether CBD could be used as an alternative therapy and treatment for cancer, pain, and inflammation.

What are the medical benefits of THC?

Although rare, cannabis-based medicines containing THC may be prescribed in the UK to relieve symptoms of certain conditions.

Circumstances in which a person might be prescribed medical cannabis include children and adults with severe or rare forms of epilepsy, adults undergoing chemotherapy, and people with multiple sclerosis (MS) dealing with muscle spasms and stiffness.

However, medical cannabis would only be considered where other treatments had not helped or had been deemed unsuitable.

Advocates of medical cannabis also claim that it can help people with mental health conditions such as anxiety and post-traumatic stress disorder. However, further research is still being undertaken in this area.

What are the side effects of CBD and THC?

Because THC and CBD have different chemical compositions, the side effects of each are also different.

People who use cannabis – which is illegal in the UK, and which contains a higher concentration of THC than CBD – have been known to experience side effects including:

  • Increased heart rate and low blood pressure
  • Problems with coordination
  • Red eyes
  • Dry mouth
  • Anxiety and distress
  • Memory loss and confusion
  • Seizures

Regular ingestion of THC (via cannabis) over a prolonged period has been linked to many other long-term physical and psychological effects.

It is also important to note that the side effects of cannabis can vary considerably and can be much more harmful, depending on the strain of the drug. This is because some strains of cannabis contain much higher levels of THC than others.

In contrast, CBD products containing less than 0.2% THC are generally considered safe and are legal to buy and sell in the UK.

This is because CBD containing less than 0.2% THC is unlikely to cause any psychoactive effects.

However, CBD still has the potential to cause adverse physical side effects, depending on how much a person uses, and whether they are taking CBD at the same time as other over the counter or prescription medications.

Some known side effects of CBD use include:

  • Dry mouth
  • Reduced appetite
  • Fatigue
  • Stomach issues
  • Dizziness
  • Nausea
  • Drowsiness

Excess use of CBD has also been linked to an increased risk of liver damage and can interfere with the effects of some prescription medications.

If you are considering taking CBD for medicinal purposes, it is recommended that you speak to your doctor in the first instance, especially if you are already taking prescribed medications.

Where can I buy a drug test?

AlphaBiolabs offers two types of home drug tests, designed to give you peace of mind or enable you to seek support for a friend or loved one who is struggling with substance misuse, including cannabis use.

  • Home Urine Drug Test Kit (£18) – this easy-to-use home drug testing kit can detect drugs and their metabolites in a urine sample. The self-contained screening kit includes built-in test strips, allowing you to read the results in just 5 minutes
  • Drug and Alcohol Nail Test (from £99) – this test can detect drug use for a period of up to 12 months prior to samples being collected, with only a sample of fingernail clippings or toenail clippings required. Simply follow the instructions included in your test kit to collect your nail clipping samples and return them to our accredited laboratory for testing

Please be aware that our home drug test kits are for peace of mind only, and the results cannot be used in court. If you require a drug test for official matters, you will need a legal drug test.

For confidential advice about which test might best suit your needs, you can also call our Customer Services team on 0333 600 1300 or email info@alphabiolabs.com.

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Marie Law

Marie Law

Head of Toxicology at AlphaBiolabs

A highly-skilled and respected scientist with over 13 years’ experience in the field of forensics, Marie joined AlphaBiolabs in 2022 and oversees the company’s growing toxicology team.

As Head of Toxicology, Marie’s day-to-day responsibilities include maintaining the highest quality testing standards for toxicology and further enhancing AlphaBiolabs’ drug and alcohol testing services for members of the public, the legal sector, and the workplace sector.

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