What Is RSO? Rick Simpson Oil, Explained Without the Hype

TL;DR

RSO — Rick Simpson Oil — is a thick, dark, whole-plant cannabis extract, usually taken orally in amounts the size of a grain of rice. It is named for the Canadian man who popularized it in the early 2000s after claiming it cured his skin cancer. That claim is anecdote, not evidence: no clinical trial has shown RSO cures cancer or any other disease. What is certain is its strength — RSO is typically a very high-THC product, and its doses should be treated with the same respect as any potent edible.

What RSO is

RSO is made by washing cannabis flower in a solvent to strip out its cannabinoids, terpenes and plant compounds, then evaporating the solvent away until only a thick, tar-like oil remains. Because the extraction uses the whole plant and keeps a broad spectrum of its compounds, RSO is often described as a full-spectrum extract — closer in spirit to a tincture-style oil than to a refined distillate (see our tincture dosage guide for how oral oils are dosed).

It is sold and used in small oral doses — classically an amount the size of a grain of rice, placed under the tongue or on food, or in capsules. It is not smoked or dabbed; the point of the format is a long-lasting, edible-style effect in a tiny volume.

The Rick Simpson story

Rick Simpson is a Canadian engineer who, in 2003, treated spots of skin cancer on his own arm with a homemade cannabis oil and reported that they disappeared. He became an evangelist for the oil, gave it away freely, and published a protocol — building up slowly from rice-grain doses to about a gram a day, roughly 60 grams over 90 days — that his followers still cite.

His story is genuinely why RSO exists and why it is famous. It is also, in evidence terms, one man's account of one case, never tested in a controlled trial. Laboratory research on cannabinoids and cancer cells exists and continues, but it is preclinical — petri dishes and animals — which is a long way from proof that an oil cures cancer in people. Anyone facing a serious diagnosis deserves that distinction stated plainly, and any decision about treatment belongs in a conversation with their oncologist, not a dispensary.

How strong is it?

Very. RSO typically tests in the high-THC range for extracts — licensed products are labeled, and it is common to see them in the region of 60–90% THC. At that concentration, the traditional rice-grain dose (roughly 20–30 mg of oil, depending on how it's measured out) can carry a dose comparable to a strong edible serving — and Simpson's full protocol dose of a gram a day is many times what a typical consumer would ever take. Onset and duration behave like an edible: effects build over 1 to 2 hours and can last 6 to 8 or longer, as we cover in how long edibles last. New users who try RSO should start with a fraction of the classic dose and wait the full onset before judging it.

RSO vs FECO

In California dispensaries you will see RSO alongside a near-twin: FECO, Full Extract Cannabis Oil. The products are functionally the same idea — whole-plant, full-spectrum, thick oral oil. The difference is the solvent and the label: FECO is specifically made with food-grade ethanol, while oil sold as RSO may be produced by Simpson's original method or with ethanol as well. Licensed versions of both are lab-tested for potency and residual solvents, which is the part that matters for safety.

A safety note on making it

Simpson's original recipe used solvents like naphtha, and the internet is full of home-extraction instructions. Be direct about this: evaporating flammable solvent is genuinely dangerous — it has caused fires and serious burns — and a homemade oil carries no test for residual solvent or potency. Whatever one's view of the oil, the licensed, lab-tested version removes both of those risks, and in California it is available through legal retailers, including delivery. If you use RSO, also treat it like the strong edible it is: don't drive, keep it away from kids and pets, and store it labeled.

Our perspective

We stock respect for what RSO is without selling the legend. It is a legitimate, useful format — a potent, long-lasting, smoke-free option that some of our customers rely on for sleep and for strong, steady effects, in a dose the size of a rice grain. What it is not is a proven medicine for the diseases attached to its name, and any seller who tells you otherwise is telling you more about themselves than about the oil. Buy it tested, start far below the famous protocol, and let it be what it demonstrably is.

FAQ

What does RSO stand for?

Rick Simpson Oil, named for the Canadian advocate who popularized the whole-plant extract in the early 2000s and gave it away while promoting his protocol.

Does RSO cure cancer?

There is no clinical evidence that it does. Simpson's claim comes from his personal account; cannabinoid research in cancer is still preclinical. RSO should never replace or delay medical treatment, and anyone considering it alongside treatment should discuss it with their doctor.

How much RSO should a beginner take?

Far less than the classic rice-grain dose to start — a fraction of it — then wait at least 2 hours. RSO is typically 60–90% THC and behaves like a strong edible with a long duration. Simpson's gram-a-day protocol was built up over weeks by his account and is not a starting point for anyone.

How is RSO taken?

Orally: under the tongue, on a small piece of food, or in capsules. It is thick and bitter, so many people put it on something with fat or strong flavor. It is not meant to be smoked or dabbed.

Is RSO legal in California?

Yes, when sold by a licensed retailer — it is tested and labeled like other cannabis products, and adults 21+ (or 18+ with a valid medical recommendation) can buy it, including through licensed delivery.

Sources

• Simpson R. Phoenix Tears — Rick Simpson's own published account of his 2003 self-treatment and the protocol he promoted (the origin of the claim; anecdotal, not clinical evidence).
• National Cancer Institute. Cannabis and Cannabinoids (PDQ) — Health Professional Version: cannabinoid anticancer research remains preclinical; no cannabis product is an approved cancer treatment.
• California Department of Cannabis Control — testing and labeling requirements for cannabis extracts sold by licensed retailers.