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Rick Simpson Oil (RSO): what it is, UK law and the risks
Rick Simpson Oil, usually shortened to RSO, is a thick, sticky cannabis extract with a very high THC content. It is a type of THC oil (also known as weed oil) and is named after Rick Simpson, a Canadian who made the oil himself and gave it away. In the UK it is a Class B drug under the Misuse of Drugs Act 1971: possessing, supplying and producing it are all criminal offences.
Many people first hear about RSO through stories about cancer. This guide explains who Rick Simpson is, what the evidence on cancer actually shows, what UK law says, why making the oil yourself is dangerous and how it differs from legal CBD oil.
RSO and CBD oil both come from the cannabis plant, but they are very different products. RSO is all about THC, the compound that causes the high and that the law restricts. CBD oil contains at most a trace of it.
Looking for a legal alternative?
Many people searching for Rick Simpson Oil really want to know what they can legally buy from the cannabis plant. If that sounds like you, CBD oil is usually the obvious next step.
Rick Simpson Oil is a concentrated cannabis extract: the active compounds are drawn out of the buds with a solvent, leaving a thick, sticky oil. In a 2013 study, researchers from the universities of Siena and Leiden called "Simpson oil" the best-known example of this type of cannabis oil.
Simpson himself claims THC levels in the 90 per cent range. No independent measurement has confirmed that, and nobody checks what a homemade or illegally sold batch really contains.
The names are often mixed up. Cannabis oil is the umbrella term for oils made from the plant. THC oil, also known as weed oil, is the high-THC version, and RSO is one kind of it. CBD oil is the version without the high.
What are the risks of such strong THC?
High doses of THC can cause a racing heart, anxiety or paranoia and, in severe cases, panic attacks or a short-lived psychosis. Be extra careful if mental illness runs in your family, if you are pregnant or breastfeeding, and if you are young. Never drive after taking THC: in England, Scotland and Wales it is an offence to drive with more than 2 micrograms of THC per litre of blood. Worried about your own or someone else's use? FRANK offers free, confidential advice on 0300 123 6600.
Who is Rick Simpson?
Rick Simpson, born in 1949, is a former engineer from Nova Scotia, Canada. By his own account, he worked in the hospital system until a head injury at work in 1997, and the prescription drugs he was given afterwards did nothing for his symptoms.
By his own account, a television documentary prompted him to ask doctors for a cannabis prescription, and they refused. He went on to grow cannabis, turn it into oil and hand the oil out free of charge until 2009, by his own account to about 5,000 people.
The story that made him famous is about skin cancer. By his own account, a doctor examined three spots in late 2002: near his right eye, on his left cheek and on his chest. In January 2003 the spot near his eye was surgically removed, and the pathology report showed basal cell carcinoma, a common skin cancer. Simpson says he treated the other two spots with his oil. That claim has never been verified by any scientific or medical body.
In 2005 police raided his property and seized 1,190 cannabis plants, and in 2007 a jury in Amherst, Nova Scotia, found him guilty of unlawful production of cannabis and of possession for the purpose of trafficking. His 2008 film Run From the Cure spread his story further. In November 2009 police raided his home again while he was in Europe, and he did not return to Canada. According to his website, he has lived in Croatia since 2013.
What does the evidence say about RSO and cancer?
RSO is widely discussed online as a possible cure for cancer, but the research does not support that. A 2022 review of published case reports found only one that mentioned RSO, and concluded that the case reports provide insufficient data to support cannabis as an anticancer agent.
Cancer Research UK does not mention RSO by name, but its message on cannabis oil is clear. The research so far has mostly used cancer cells in the lab or animals, with mixed results, so we do not know whether cannabinoids can treat cancer in people. Under some circumstances, cannabinoids can even encourage cancer cells to grow. Claims of solid "proof" that cannabis can cure cancer are, in the charity's words, highly misleading.
Where cannabis-based medicines do play a role in cancer care, it is in easing symptoms. Cancer Research UK notes that cannabinoids have helped some people with sickness and pain, and the NHS lists adults with nausea or vomiting caused by chemotherapy among the few groups likely to be prescribed medical cannabis, when other treatments have not helped.
Can you use RSO instead of cancer treatment?
No. Never stop or replace your treatment. Cancer Research UK warns that homemade preparations, particularly cannabis oil, carry further risks, and that people who rely on them may miss out on treatment that could save or significantly lengthen their life. The 2022 review notes that the RSO book even advises patients to stop standard treatments such as chemotherapy.
THC and CBD can also affect how other medicines work, so the NHS advises always discussing possible interactions with a specialist. If you have cancer and are thinking about cannabis, talk to your oncologist or GP first, and ask about clinical trials you may be able to join.
Is Rick Simpson Oil legal in the UK?
No. Cannabis and cannabis resin are Class B drugs under the Misuse of Drugs Act 1971, and so are THC and any preparation that contains it. RSO is a THC-rich cannabis preparation, so it falls under Class B. As Cancer Research UK puts it: cannabis oil is illegal in the UK.
There is one legal route to THC: cannabis-based products for medicinal use. Since 1 November 2018, doctors on the GMC specialist register have been able to prescribe them; on the NHS, that means a specialist hospital doctor or someone working under their supervision. Homemade or illegally sold RSO is not one of these medicines.
Can you buy or order RSO?
Not legally. Anyone selling RSO to UK customers is operating outside the law. The NHS warns that many cannabis-based products sold online are of unknown quality and content, may be illegal and could be dangerous. Cancer Research UK adds that scammers take money from cancer patients and their families for "cannabis oil" that never arrives. Even Simpson, who says he does not sell oil himself, warns that many suppliers use his name and often sell sub-standard oil at a very high price.
How is RSO made, and why is making it yourself dangerous?
Simpson's method uses a large amount of cannabis and a flammable solvent, which is evaporated off until a thick oil remains. We deliberately do not describe the method, for three reasons.
Fire and explosion. Solvent vapours can build up in a poorly ventilated room, where a naked flame or pilot light can ignite them. The New Jersey State Fire Marshal describes the risk of fire or explosion when extracting cannabis with flammable solvents as great. One US burns centre treated 101 patients with burns from making cannabis extracts with a flammable solvent between 2007 and 2014, and three of them died.
The law. Making RSO means possessing a large quantity of cannabis and producing a Class B drug, which carries up to 14 years in prison.
A product nobody checks. Homemade oil never goes through a lab. Researchers who made oil following Simpson's method found significant solvent residues in it, and again in a sample a patient had made to treat their own cancer. Both solvents used in those Simpson-style extracts are listed as potential cancer hazards on their own safety data sheets. Strength is just as unpredictable: in a 2024 study, the THC content of homemade cannabis oils ranged from 0 to 388 mg per ml.
Rick Simpson Oil or CBD oil: the differences
RSO and CBD oil come from the same plant, but they act differently and UK law treats them very differently.
Property
Rick Simpson Oil (RSO)
CBD oil
Active substance
Mainly THC, in very high concentrations
Mainly CBD, with at most a trace of THC
Effect
Strong high that is hard to predict
No high
Status in the UK
Class B drug; possessing, supplying and producing it are criminal offences
Legal as an "exempt product", sold in shops and online
Quality control
None; homemade or sold illegally
Can be checked batch by batch through lab reports
The difference lies in the endocannabinoid system, a network of receptors in the brain and throughout the body. THC binds strongly to the CB1 receptors, especially in the brain, and that causes the high. CBD barely binds to them, which is why it does not get you high. Read more in receptors in the human body and the three main differences between CBD and THC.
Is CBD oil a treatment for cancer?
No. Cancer Research UK's conclusion applies to CBD as well: we do not know whether cannabinoids can treat cancer in people. In the UK, CBD is regulated as a novel food, not a medicine, and the Food Standards Agency does not recommend it for people on medication unless a doctor advises it.
Sources
This page is for information only. It is not medical or legal advice and contains no instructions for making cannabis products. Accessed on 11 October 2026:
