RSO, or Rick Simpson Oil, is a thick, dark cannabis extract known for its very high THC concentration, sometimes reaching up to 90%. It was popularized by Rick Simpson, a Canadian engineer and cannabis activist who claimed the oil cured his basal cell skin cancers. Since then, RSO has gained a devoted following online, particularly among people seeking alternative cancer treatments, though no clinical evidence supports those claims.
How RSO Is Made
RSO is produced by soaking cannabis plant material in a strong solvent, most commonly food-grade ethanol, to pull out as many active compounds as possible. The solvent is then slowly evaporated away, leaving behind a thick, tar-like oil. The result is a full-spectrum extract, meaning it contains not just THC but also other cannabinoids like CBG, CBC, and CBN, along with terpenes, flavonoids, chlorophyll, and various plant compounds. This broad chemical profile is what distinguishes RSO from more refined cannabis products like distillates, which strip away most of those extras.
Because RSO was originally a homemade preparation, quality can vary enormously. Improper evaporation may leave residual solvents in the final product, which is a real safety concern with DIY batches. Commercially produced RSO sold through licensed dispensaries is generally tested for contaminants, making it a safer option than anything made at home.
RSO vs. CBD Oil
The most common point of confusion is the difference between RSO and CBD oil, and it’s a big one. RSO is loaded with THC and will get you high. CBD oil is non-intoxicating. Full-spectrum CBD products contain only trace amounts of THC (less than 0.3%), while broad-spectrum CBD and CBD isolate contain even less or none at all.
The extraction methods also differ. CBD oil is most often produced using CO₂ extraction, a cleaner, solvent-free process. RSO relies on ethanol soaking, which pulls a wider range of plant material into the final product. That’s why RSO is darker, thicker, and has a stronger taste than most CBD oils. If you’re looking for symptom relief without intoxication, CBD oil is the relevant product. RSO is specifically sought out for its potency.
How People Use RSO
RSO is consumed in several ways, each with a different onset time and intensity:
- Under the tongue (sublingual): Placing a small amount under the tongue is one of the most popular methods. The oil absorbs through the thin tissue there, reaching the bloodstream relatively quickly and bypassing the digestive system.
- Mixed with food: Many people add RSO to food or drink. When swallowed, it passes through the digestive tract and is processed by the liver, which converts THC into a more potent form. This means stronger effects but a slower onset, often 45 minutes to two hours.
- Capsules: For more precise dosing, RSO can be measured into gelatin or vegetarian capsules. The experience is similar to eating it with food.
- Applied to skin: Some users apply RSO directly to the skin for localized pain, inflammation, or skin conditions. Topical application doesn’t produce intoxication.
The Original RSO Protocol
Rick Simpson’s recommended regimen calls for consuming 60 grams of RSO over a 90-day period. Users start with a very small dose, roughly the size of a grain of rice, and gradually increase until they reach about 1 gram per day. The idea behind this slow ramp-up is to build tolerance to the psychoactive effects, which can be overwhelming at higher doses for anyone not accustomed to THC.
Simpson originally directed this protocol at cancer patients and went so far as to advise people to stop conventional treatments like chemotherapy. That recommendation is not supported by medical evidence and carries serious risk.
What the Research Actually Shows
RSO’s reputation as a cancer treatment has spread widely online, but the clinical picture is thin. A review published in Cannabis and Cannabinoid Research examined the available human data and found that no strong clinical trial evidence confirms that cannabinoids have anticancer effects in people. Only two phase I clinical trials have been published. One tested THC in patients with recurrent brain tumors and found no improvement in tumor control or survival. A second, smaller feasibility study using a THC/CBD spray alongside chemotherapy did observe improved survival in the cannabis group, but the study wasn’t designed to draw survival conclusions.
The case reports cited in pro-RSO literature are, in the words of the review’s authors, “vague and provide little clinical evidence to substantiate any anticancer claims.” The National Academies of Sciences, Engineering, and Medicine concluded that there is insufficient evidence to support or refute the idea that cannabinoids effectively treat any cancer, including brain cancers. None of this means cannabinoids are useless in oncology. Some patients use cannabis products alongside conventional treatment for symptom management, including nausea, pain, and appetite loss. But that’s a very different claim than curing cancer.
Side Effects and Risks
Because RSO can contain THC concentrations as high as 90%, the psychoactive effects are intense, especially for new users. Common side effects include anxiety, paranoia, dizziness, impaired memory, rapid heart rate, and extreme sedation. At the doses called for in the Simpson protocol (up to 1 gram per day), these effects can be debilitating even for experienced cannabis users during the early stages of the regimen.
There’s also the issue of what else might be in the oil. Homemade RSO carries a risk of residual solvent contamination if the ethanol isn’t fully evaporated. Pesticides, heavy metals, and mold from the source cannabis can also concentrate in the final product. If you’re considering RSO, purchasing from a licensed dispensary with third-party lab testing significantly reduces these risks.
Legal Status
Cannabis remains a Schedule I substance under federal law in the United States, which technically makes RSO illegal at the federal level regardless of where you live. At the state level, the landscape is different. As of mid-2025, 40 states, three territories, and Washington, D.C. allow some form of medical cannabis use. Many of these states have patient registries that offer legal protection for possessing cannabis products up to a certain amount. In states with adult-use (recreational) cannabis laws, RSO is often available at dispensaries without a medical card. Your ability to legally purchase RSO depends entirely on your state’s laws.