Rick Simpson Oil, commonly called RSO, is a thick, dark cannabis extract with very high THC concentrations. People use it primarily for cancer-related symptoms, chronic pain, inflammation, and nausea, though it has also gained attention as a claimed cancer treatment. RSO differs from most CBD oils and standard cannabis products because it retains the full spectrum of compounds from the cannabis plant, with THC as the dominant ingredient.
What RSO Actually Is
RSO is made by soaking cannabis buds in a solvent, typically ethanol or naphtha, which strips the plant’s active compounds into a liquid. The solvent is then boiled off, leaving behind a thick, tar-like oil that’s usually very dark green or black. The result is a concentrated extract where THC levels can reach 60 to 90 percent, far higher than what you’d find in a typical edible or tincture.
The oil is named after Rick Simpson, a Canadian who claimed he used homemade cannabis oil to treat his own skin cancer in the early 2000s. He then promoted a specific extraction method and dosing protocol online, and the name stuck. RSO became shorthand for any high-THC, full-spectrum cannabis oil made using a similar process.
Common Uses
The most widely discussed use for RSO is cancer, both as a way to manage treatment side effects and, more controversially, as a proposed treatment for the disease itself. Many people turn to RSO hoping it will shrink tumors or slow cancer progression. Others use it specifically for the nausea and vomiting that come with chemotherapy, for appetite stimulation, or for cancer-related pain that hasn’t responded well to other approaches.
Beyond cancer, people use RSO for chronic pain conditions, severe inflammation, insomnia, and anxiety. Because the oil is so concentrated, even a tiny amount delivers a potent dose of THC, which is why some users with serious or treatment-resistant symptoms prefer it over lower-strength cannabis products. The high THC content also means it produces strong psychoactive effects, especially at larger doses.
What the Research Actually Shows
This is where RSO’s reputation runs well ahead of the science. No clinical trials have tested RSO as a cancer treatment in humans. The National Cancer Institute states plainly that highly concentrated THC oil extracts “have not been evaluated in any clinical trials for anticancer activity or safety.” A search of published medical literature turns up no ongoing clinical trials of cannabis as a direct cancer treatment.
The one small pilot study that did test THC in cancer patients, injecting it directly into recurring brain tumors, found no significant clinical benefit. Lab studies on cancer cells and animal models have shown more intriguing results. THC can bind to specific receptors on certain cancer cells, particularly in brain cancers, and trigger processes that reduce cell growth and promote cell death in a controlled setting. But effects in a petri dish or a mouse don’t reliably translate to effects in a human body, and no one has demonstrated that swallowing RSO delivers these compounds to tumors in meaningful concentrations.
Where cannabinoids do have established medical value is in symptom management. The FDA has approved synthetic THC-based medications for chemotherapy-induced nausea and vomiting in patients who haven’t responded to standard anti-nausea drugs. This supports the idea that THC can help with these symptoms, but it’s a different claim from saying RSO treats cancer itself.
How People Take RSO
RSO comes in syringes (for dosing, not injection) and is typically used in three ways.
- Swallowed with food: The most common method. You place a very small amount, no larger than half a grain of rice, onto a bite of food, ideally something with some fat to help absorption. Effects take 1 to 2 hours to kick in and last several hours.
- Under the tongue: Placing a small drop under your tongue and holding it for 30 to 60 seconds before swallowing allows some of the THC to absorb directly into the bloodstream, which can produce faster effects than swallowing alone.
- On the skin: Some people apply RSO directly to skin conditions or localized pain. A small amount is placed on the area and covered with a bandage to keep it in place. Topical use generally doesn’t produce the same psychoactive effects as ingestion.
The standard advice from experienced users is to start extremely small. RSO is far more concentrated than most cannabis products, and taking too much on the first try can produce overwhelming sedation, anxiety, or paranoia. Proponents of RSO for cancer typically describe a gradual ramp-up schedule over weeks, slowly increasing the dose as tolerance builds.
Side Effects and Risks
The side effects of RSO are essentially the side effects of consuming large amounts of THC: drowsiness, impaired coordination, altered perception of time, dry mouth, and red eyes at lower doses. At higher doses, which RSO makes easy to reach, the risks escalate. High THC intake can trigger intense anxiety, paranoia, rapid heart rate, and disorientation, particularly in people who aren’t experienced with cannabis or who are sensitive to THC.
There’s also a drug interaction concern that often goes unmentioned. Concentrated cannabis oils can interfere with the liver enzymes that process many common medications. This means RSO could potentially increase the toxicity of certain drugs or reduce their effectiveness, a serious issue for anyone undergoing cancer treatment with chemotherapy or targeted therapies. The National Cancer Institute specifically flags this risk with highly concentrated cannabis oils used alongside conventional treatments.
The mental health effects of sustained high-THC use are not well understood either, and people with a history of psychosis, bipolar disorder, or severe anxiety disorders face additional risks from products this potent.
Manufacturing and Quality Concerns
Because RSO originated as a homemade product and is still produced outside pharmaceutical oversight in most places, quality control is a real concern. The extraction process uses solvents to pull active compounds from the plant, and if those solvents aren’t fully removed, they end up in the final product.
The most common solvents in cannabis extraction are ethanol, butane, and carbon dioxide. Each carries different risks if residues remain. Butane inhalation at high levels has been linked to cardiac damage and organ failure. Benzene, which can appear as a contaminant in some solvents, is a known carcinogen that affects bone marrow. Other residual compounds like xylenes and hexane can cause nausea, headaches, dizziness, and depression of the central nervous system.
In states with regulated cannabis markets, lab-tested RSO products from licensed dispensaries undergo residual solvent testing, which significantly reduces this risk. Homemade RSO or products purchased from unregulated sources carry no such guarantee. If you’re considering RSO, products from a licensed dispensary with a certificate of analysis showing solvent levels are a meaningfully safer option than anything made at home or bought informally.
RSO vs. Other Cannabis Oils
RSO is often confused with CBD oil, but they’re fundamentally different products. CBD oil is typically derived from hemp, contains little to no THC, and doesn’t produce a high. RSO is THC-dominant and intensely psychoactive. CBD oil is legal federally in the U.S., while RSO’s legality depends on your state’s cannabis laws.
RSO also differs from most commercial cannabis concentrates because it’s designed to preserve the full range of the plant’s compounds, including minor cannabinoids, terpenes, and flavonoids, rather than isolating a single cannabinoid. Proponents believe this “full-spectrum” profile creates a stronger therapeutic effect than any single compound alone, though this theory hasn’t been rigorously tested in clinical settings with RSO specifically.