Cannabis oil and cancer

Find out about cannabis, CBD oil and cancer, finding reliable information online, and about cannabis oil and the difference between THC and CBD.

What is cannabis?

Cannabis is a plant. It produces a resin that contains different substances. Some of these may have medicinal value. These substances are called cannabinoids.

2 of the main cannabinoids are:

  • THC (delta-9-tetrahydrocannabidiol)
  • CBD (cannabidiol).

THC is a psychoactive substance. This means it can affect your mood and how you feel so that you feel ‘high’ or ‘stoned’. CBD does not cause these effects.

You have probably heard many names for cannabis. These include marijuana, hemp, pot, grass and hash. Cannabis has been used both medicinally and recreationally for thousands of years.

Different types of cannabis contain different amounts of THC and CBD. For example, hemp comes from a cannabis plant that contains only a very small amount of THC. Hemp oil is used as a food supplement or in products like soaps.

Cannabis and the law

Cannabis is classified as a class B drug in the UK. This means it is illegal to have it or sell it. The laws about cannabis mean that:

  • cannabinoid THC and products that contain THC are illegal in the UK
  • CBD is legal.

Cannabis and medicines

There are some medicines available in the UK that come from cannabis. These include:

These medicines go through a process to make sure they are safe to be licensed in the UK. This is the same process that is used to decide whether any medicine can be prescribed in the UK.

Medicinal cannabis (also called cannabis-based products for medicinal use) was legalised in the UK in November 2018. This means it can be prescribed by specialist doctors for certain medical conditions. These conditions include rare, severe forms of epilepsy and severe spasticity (muscle stiffness and spasms) caused by multiple sclerosis. Medicinal cannabis cannot currently be prescribed for cancer or pain.

Cannabis and cancer

There is a lot of interest in the possible effects of cannabinoids on cancer. Some people claim that using CBD has had a positive effect on their health. But these are individual stories, not scientific evidence. There is no way of checking whether the stories are reliable, or finding out what other treatments the person has had.

Scientists have researched THC and CBD to see if they could have any role in the treatment of cancer. Most of this research is at a very early stage and still being done in the laboratory.

There have been some small studies in people. Research continues to see if cannabis-based medicines could help in the treatment of some cancers or symptoms. But at the moment, there is no reliable, medical evidence to show whether cannabis, in any form, can effectively and safely treat cancer in humans.

What does the research say?

Research has found that cannabinoids can:

  • cause a cell to die
  • stop cells from dividing
  • stop cells from developing new blood vessels.

But it has also found that cannabinoids can:

  • damage important blood vessels
  • encourage cancer cells to grow in some situations
  • make the immune system less effective – the immune system fights diseases such as cancer.

It is possible that cannabis may have an effect in treating some types of cancer. But it may make other types of cancer grow or spread more quickly.

Research has also looked at how using cannabis may affect the risk of developing cancer. This has produced different results. Some studies show that using cannabis may help reduce the risk of developing cancer. But there are also studies that show it increases the risk of cancer.

Because of these mixed results, experts feel there needs to be more research into the chemicals found in cannabis and their possible benefits.

Cannabis oil and CBD oil

Many types of cannabis oil and CBD oil are sold online. Cannabis oil can contain different amounts of THC and CBD.

CBD oil is also sold in some shops, such as health food shops. CBD oil in its pure form does not contain THC. This means it does not have any psychoactive effects (it does not make you feel stoned).

CBD oil is not a controlled substance under the Misuse of Drugs Act. It can be sold in the UK as a food supplement, if the seller does not make any claims about its medicinal properties.

There are different ways of taking CBD oil. These include a liquid that you put under your tongue, or capsules that you swallow.

Understandably, many people want to try anything that may help treat cancer, particularly if things are not going well with conventional cancer treatments. This could be if they have cancer themselves, or if a loved one has cancer.

But if you are thinking about using CBD oil, there are some important things to consider.

Effects of CBD oil on cancer treatment

It is important to talk to your cancer doctor before using CBD oil. CBD can affect some cancer treatments, and your cancer doctor needs to know about any possible effects or side effects you might have.

Buying cannabis products online

Buying cannabis products, including CBD oil, online can be risky. They are not regulated, so often the quality and what is in them is not known.

In 2017, a researcher tested 84 CBD products sold online. The results showed that:

  • about 1 in 4 (26%) contained less CBD than stated on the label
  • almost half (48%) contained more CBD than stated on the label
  • more than 1 in 5 (21%) contained THC.

Side effects of cannabis oil

There are side effects of using cannabis oil. THC can:

  • increase your heart rate
  • cause dizziness, hallucinations and paranoia
  • make you feel stoned.

Effects on other medicines

CBD and THC can affect how some medicines work.

Finding reliable information online

If you are looking for information online, you need to know that it is accurate and up to date.

Here are some things to think about when you are looking at a website:

  • Is the information regularly updated? You should be able to find the date when the information was last reviewed on each page.
  • Is it clear who has written the information? A good website should tell you about the organisation that has made the pages or written the information.
  • Are there references? The website should list the sources it used to write the information, or tell you who to contact to find out.
  • Is the website sponsored by a company? If so, it might mean the information is biased towards that company’s products or services.

The National Cancer Institute's (NCI) and Cancer Research UK have more detailed information about cannabis.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Dr Saul Berkovitz.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 01 April 2022
Next review: 01 April 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.