RSO, short for Rick Simpson Oil, is a thick, dark cannabis extract that contains high levels of THC and is made by soaking cannabis plant material in a solvent like ethanol. It’s a full-spectrum extract, meaning it retains the plant’s full range of cannabinoids, terpenes, and flavonoids rather than isolating a single compound. RSO typically has a THC concentration in the 40 to 60% range, making it significantly more potent than dried cannabis flower.
Where RSO Came From
RSO is named after Rick Simpson, a Canadian engineer and cannabis activist who gained attention in the early 2000s for claiming that a homemade cannabis oil helped treat basal cell skin cancers on his arm. Simpson went on to publicly share his extraction method and advocate for cannabis oil as a treatment for cancer and other conditions. His claims spread widely online, and the oil became one of the most discussed cannabis products in alternative health circles.
How RSO Is Made
The basic process involves soaking cannabis flower in a strong solvent, most commonly ethanol (grain alcohol), to strip out the plant’s active compounds. The solvent is then evaporated off, leaving behind a thick, tar-like oil that’s nearly black or very dark green in color. This crude extraction method pulls out essentially everything from the plant: THC, CBD, minor cannabinoids, terpenes, chlorophyll, and plant waxes. That chlorophyll and wax content is what gives RSO its distinctive dark color and bitter taste, and it’s one reason the oil looks so different from the golden, refined concentrates you might see at a dispensary.
RSO is not meant to be smoked or vaped. Its thick consistency makes it incompatible with those methods. Instead, it’s typically sold in oral syringes for precise dosing.
How People Use It
There are three main ways people take RSO. The most common is sublingual: placing a very small amount (roughly half the size of a grain of rice to start) under the tongue, holding it for 60 to 90 seconds, then swallowing. The tissue under your tongue absorbs cannabinoids directly into the bloodstream, so effects can kick in within 15 to 45 minutes.
The second method is mixing RSO into food. When swallowed and processed through the digestive system, the effects take longer to appear but tend to be more intense and longer-lasting. Pairing RSO with a fat source like butter or coconut oil can improve absorption. The third option is topical application, where the oil is spread directly on the skin, though this is less common and delivers cannabinoids locally rather than throughout the body.
Because the oil is so thick, warming the syringe slightly between your hands makes it easier to dispense. A practical tip: stop squeezing just before you reach the dose you want, since the oil tends to keep dripping. Pulling the plunger back gently will draw any excess back in.
RSO vs. CBD Oil
This is where people get confused, and the difference matters. RSO is loaded with THC and will get you high. CBD oil is extracted from hemp plants that are naturally low in THC (less than 0.3% by law) and is non-intoxicating. They come from the same plant species but are fundamentally different products with different effects.
CBD oil also comes in several forms. Full-spectrum CBD contains trace amounts of THC alongside other cannabinoids. Broad-spectrum CBD has those other cannabinoids but with the THC removed entirely. CBD isolate is pure CBD with nothing else. None of these will produce the intense psychoactive effects of RSO.
The extraction methods differ too. CBD oil is often produced using CO₂ extraction, a cleaner, solvent-free process that yields a more refined product. RSO’s ethanol soak is a rougher technique that prioritizes pulling out the maximum amount of plant material, which is why the end product is darker, thicker, and more complex in its chemical makeup.
What the Cancer Research Actually Shows
RSO’s reputation is built largely on claims that it can treat or cure cancer. The reality is that no strong clinical trial data exist to confirm these claims. A 2022 review published in the National Institutes of Health database examined the available evidence and found that only one published case report even involved RSO specifically. The case reports cited by Simpson and his supporters are described as vague, providing little clinical evidence to back up anticancer claims.
Some preclinical research (lab and animal studies) has suggested cannabinoids could have anticancer properties, but that’s a long way from proving they work in humans. The only published human trials involving THC and cancer were two small Phase I studies focused on a specific type of brain tumor, and neither of those used RSO. Simpson’s own protocol suggests ingesting 60 grams of RSO over 90 days, but this recommendation is not supported by clinical evidence.
Side Effects and Risks
Because RSO contains THC concentrations far above what you’d get from smoking or eating a typical edible, the side effects can be significant. Short-term effects of high-dose THC include impaired short-term memory, altered sense of time, poor motor coordination, impaired judgment, and in high doses, paranoia and psychosis. These effects are dose-dependent, and RSO makes it easy to consume a large amount of THC quickly, especially for someone without tolerance.
Long-term heavy use of THC carries additional concerns. Roughly 9% of regular cannabis users develop a dependency, and that number climbs to 17% for people who start using in adolescence and 25 to 50% for daily users. Heavy, sustained use is also associated with increased risk of anxiety and depression. For people with a genetic predisposition to psychotic disorders like schizophrenia, high-potency cannabis can worsen the disease course or advance the timing of a first psychotic episode by two to six years.
The potency issue is worth emphasizing. THC content in cannabis has risen from about 3% in the 1980s to 12% in typical flower by 2012, and concentrated products like RSO push well beyond that. Higher potency correlates with more emergency department visits and greater risk of adverse psychological effects.
Legal Status
RSO’s legal status depends entirely on where you live. Because it contains high levels of THC, it falls under cannabis regulations rather than hemp regulations. In the United States, the Justice Department and DEA recently moved FDA-approved marijuana products and state-licensed medical marijuana products to Schedule III of the Controlled Substances Act, a less restrictive classification than the previous Schedule I. However, RSO as a product is not FDA-approved, so its legality hinges on your state’s cannabis laws. In states with legal medical or recreational marijuana programs, RSO is commonly available at licensed dispensaries. In states without those programs, possessing it remains illegal under both state and federal law.