Rick Simpson Oil (RSO) is a highly concentrated cannabis extract that some people use alongside or instead of conventional cancer treatment. It contains up to 90% THC and retains the full range of compounds found in the cannabis plant. Despite widespread claims online, no clinical trials have tested RSO as a cancer treatment in humans, and no medical organization recommends it as a cure. That said, the story is more nuanced than a simple yes or no.
What RSO Actually Is
RSO is named after Rick Simpson, a Canadian who claimed he cured his own skin cancer with a homemade cannabis extract in the early 2000s. The oil is made by soaking cannabis flower in a solvent (traditionally naphtha or isopropyl alcohol) to strip out the plant’s active compounds, then boiling off the solvent to leave behind a thick, dark, tar-like oil. Unlike CBD oil, which isolates one compound at low concentrations, RSO is a full-spectrum extract with extremely high THC levels.
That potency is the defining feature. Where a typical cannabis edible might contain 5 to 10 milligrams of THC per dose, RSO users following the original protocol aim to consume up to 1 gram of oil per day, with THC concentrations reaching 90%. This makes it one of the most potent cannabis products available.
The 90-Day Protocol
The standard RSO regimen calls for consuming 60 grams of oil over a 90-day window. Users start with a very small dose, roughly the size of a grain of rice, taken three times daily. Over the first few weeks, the dose gradually increases as tolerance builds, eventually reaching about 1 gram per day. The idea is to maintain consistently high cannabinoid levels in the body throughout the treatment period.
This protocol was never designed by a doctor or tested in a clinical setting. It comes directly from Rick Simpson’s personal recommendations, shared through a documentary and website. There is no published data showing this specific regimen produces anti-cancer effects in humans.
What Lab Research Shows
The reason RSO generates so much interest is that cannabinoids, particularly THC and CBD, do show anti-cancer activity in laboratory and animal studies. CBD has been shown to trigger programmed cell death in cancer cells, halt the cell division cycle, reduce the growth of new blood vessels that tumors need to feed themselves, and slow the spread of cancer cells to new locations. THC appears to work through some of the same pathways.
These findings are real, but they come with an important caveat: killing cancer cells in a petri dish is very different from shrinking a tumor inside a living person. Many substances that destroy cancer cells in the lab, including common household bleach, never become cancer treatments because they can’t be delivered safely and selectively in the human body. The leap from lab results to a proven therapy requires human clinical trials, and according to the National Cancer Institute, no clinical trials of cannabis as a cancer treatment in humans have been completed or are currently underway.
Where Cannabis Does Help Cancer Patients
While the evidence for RSO as a cancer cure is absent, the evidence for cannabis as a supportive care tool is much stronger. THC-based medications are already approved for managing chemotherapy side effects. Synthetic THC provides relief from nausea, vomiting, and the severe appetite loss that many cancer patients experience. A mouth spray combining THC and CBD has been shown to reduce cancer-related pain compared to placebo, with measurable improvements appearing as early as three weeks into treatment.
These benefits matter enormously for quality of life during cancer treatment. Many oncologists are open to discussing cannabis for symptom management, even if they would not recommend RSO as a replacement for chemotherapy, radiation, or surgery.
Risks of High-Dose THC
Taking the amounts of THC called for in the RSO protocol is not a mild experience. Common side effects include significant dizziness, memory impairment, anxiety, paranoia, and sedation. For people who are not regular cannabis users, the first weeks of escalating doses can be intensely disorienting.
A more serious concern involves drug interactions. Your liver processes both THC and many chemotherapy drugs using the same enzyme systems. Cannabinoid compounds can inhibit specific enzymes responsible for breaking down certain chemotherapy agents. One well-studied example is cyclophosphamide, a widely used chemotherapy drug with a narrow margin between an effective dose and a toxic one. If cannabinoids slow the breakdown of that drug, blood levels can rise to dangerous concentrations. Anyone receiving chemotherapy who is also using RSO may be unknowingly altering how their treatment works, potentially making it less effective or more toxic.
Safety Concerns With Homemade RSO
Because RSO is not a regulated pharmaceutical product, many users make it at home or purchase it from unregulated sources. The extraction process traditionally uses harsh solvents like naphtha or isopropyl alcohol, both of which are hazardous to ingest. Even after the solvent is boiled off, trace amounts remain in the finished oil. Isopropyl alcohol is a component of industrial cleaners and is toxic when consumed. Naphtha is a petroleum-based solvent with its own set of health risks.
Some producers use food-grade ethanol (the same alcohol found in spirits) as a safer alternative, but there is no standardized production process and no way to verify potency or purity without laboratory testing. Homemade RSO can vary wildly in THC content, contain residual solvents, or include contaminants like pesticides and heavy metals from the source plant material.
Why the Claims Persist
RSO’s reputation as a cancer cure rests almost entirely on anecdotal reports: people who used RSO and saw their cancer improve or disappear. These stories are compelling but unreliable as evidence. Some of these individuals were also receiving conventional treatment at the same time. Others may have had cancers that went into spontaneous remission, which occurs rarely but does happen. Without controlled studies comparing RSO users to non-users while holding all other variables constant, it is impossible to know whether the oil played any role.
The National Cancer Institute has stated plainly that highly concentrated THC and CBD oils are “illegally promoted as potential cancer cures” and have not been evaluated in any clinical trials for anti-cancer activity or safety. This does not mean cannabinoids will never prove useful in oncology. It means the current evidence does not support using RSO as a cancer treatment, and people who choose it over proven therapies are taking a significant and unmeasured risk.
The Practical Bottom Line
RSO is a potent, full-spectrum cannabis extract with legitimate uses for symptom relief but no proven ability to treat cancer in humans. The biological mechanisms that make cannabinoids interesting to cancer researchers are real, but they have not translated into clinical results. If you are considering RSO, the most important thing you can do is be honest with your oncologist about it, particularly because of the potential for serious drug interactions with chemotherapy. Using RSO for nausea, pain, or appetite alongside conventional treatment is a conversation worth having with your care team. Replacing proven cancer treatment with RSO is a different decision entirely, and one that the current evidence does not support.