What is RSO? RSO, short for Rick Simpson oil, is a thick, dark cannabis extract made from the whole flower of THC-rich plants. Instead of isolating one compound, it keeps most of what the flower contains, so it is potent and strongly intoxicating. RSO became famous through bold cancer claims, and those claims rest on personal stories, not clinical trials. Here's what it is, how it's made and taken, and what research does and doesn't show.
What is RSO? A full-extract, high-THC oil
RSO belongs to a family of products called full-extract cannabis oil, or FECO, and some shoppers simply call it RSO oil. Makers soak cannabis flower in a solvent, strain out the plant material and remove the solvent, leaving a sticky, tar-like oil. The name describes a style of extract, not a brand.
Because it starts with THC-dominant flower, RSO packs a lot of THC into a little oil. It usually comes in a syringe, since it's too thick to pour, so the milligram count on the label is the number to read first. Our guide to shopping for RSO walks through syringe labels and testing details.
Rick Simpson's story and the claims around it
The oil is named for Rick Simpson, a Canadian medical cannabis activist best known for popularizing cannabis oil as a home remedy for skin cancer. In 2003, he claimed that a high-THC oil he extracted himself cured his basal cell carcinoma, a common type of skin cancer. Retellings of the story differ on the details, and the claim rests on his own account, but it spread widely online, including through a documentary about him.
One account, however moving, can't show cause and effect. A single story leaves other explanations for what happened wide open. That's why researchers rely on controlled trials, and why RSO has never been approved as a cancer treatment.
Cannabinoids and cancer: what lab studies show
Lab research gives the cancer claims their scientific gloss. In cell and animal studies reviewed by the National Cancer Institute, cannabinoids killed some tumor cells while sparing normal ones, and some animal studies showed tumors shrinking. Those are early findings, and plenty of compounds that look promising in a dish never work in people.
Human evidence is where the story falls apart. The National Cancer Institute notes that highly concentrated THC and CBD oils are illegally promoted as potential cancer cures, even though they have never been evaluated in clinical trials for anticancer activity or safety. A 2022 review of 77 published case reports judged most of them too weak to support an anticancer effect and found no strong clinical trial data behind the lab results. The FDA has not approved cannabis or cannabinoids as a cancer treatment.
The bottom line: RSO has never been tested against cancer in a clinical trial, and there is no trial evidence that it shrinks tumors or works against cancer in people. Don't swap or delay cancer care for it.
Where the evidence is stronger: approved cannabinoid medicines
Some cannabinoid medicines do have solid backing for specific uses. The FDA has approved dronabinol, a synthetic form of THC, for nausea caused by cancer chemotherapy and for appetite loss tied to weight loss in people with AIDS. It has also approved nabilone, a lab-made compound similar to THC, for chemotherapy nausea.
These are pharmacy medicines with measured doses, tested in clinical trials. RSO isn't one of them, and the FDA has not approved cannabis itself for any disease or condition. If nausea or appetite is a struggle during cancer care, ask your oncology team about the options that have been studied.
RSO vs CBD oil: how they differ
| RSO | Typical CBD oil | |
|---|---|---|
| Starting plant | THC-dominant cannabis flower | Usually hemp |
| Main cannabinoid | THC | CBD |
| Intoxicating? | Yes, strongly | Not the way THC is |
| Texture | Thick, sticky paste | Thin oil, often mixed with a carrier oil |
| Usual package | Syringe | Dropper bottle |
Some products blend the two, such as RSO made with a set ratio of THC to CBD, so check the milligrams of each on the label.
How licensed processors make RSO
Licensed processors follow the same basic idea at a larger scale: soak, strain, then remove the solvent. Ethanol is a common choice, and it is evaporated off to leave the concentrated oil. Extraction solvents like ethanol are flammable, a big reason extraction belongs in licensed facilities rather than home kitchens.
Every product on our shelves comes from trusted vendors and has passed Michigan testing. For a wider look at the process, see our overview of cannabis extraction methods.
How to use RSO: common ways people take it
Most people take RSO by mouth:
- On or under the tongue: a very small amount squeezed from the syringe.
- In food: stirred into a spoonful of something, like peanut butter.
- In capsules: some products come pre-measured.
- On skin: some people apply it topically, though topical use hasn't been well studied.
RSO isn't made for smoking. Swallowed THC is absorbed slowly and processed by the liver, which turns some of it into another potent compound, so it takes longer to kick in than inhaled cannabis and lasts longer, too. Our guide to how THC works in the body explains why.
RSO side effects, and starting small
Because RSO is concentrated THC, its effects can be strong. The National Cancer Institute lists possible cannabis side effects including a fast heartbeat, low blood pressure, dizziness, drowsiness and, for some people, paranoia or hallucinations. Concentrated cannabinoids can also interact with medicines: the institute notes that CBD may block liver enzymes that process many drugs, including some cancer therapies.
There's no standard RSO dosage, and syringes vary widely in strength. If you and your doctor decide it's worth trying:
- Start with the smallest amount you can measure.
- Wait before taking more, because swallowed THC builds slowly.
- Don't drive or operate machinery after using it.
- Store syringes locked up, out of reach of children and pets.
RSO is for adults 21+, or patients 18+ with a Michigan medical card. Please consume responsibly.
Talking to your doctor, and Michigan's medical program
Talk with your doctor before using RSO, and with your oncologist if you're in cancer care. That matters even more if you're pregnant or breastfeeding, take other medicines, or have heart, liver or mental health conditions.
Michigan's medical marijuana program lists cancer among its qualifying conditions. A medical card is a legal status, though, not a sign that cannabis will help a particular condition. Our pages on getting a Michigan medical card and the patient guide explain the process.
Registered patients 18 and older with a valid card are welcome at High Society. If you have a question about a product label, find your nearest store and ask our team in person.
