Rick Simpson Oil, widely known as RSO, is a thick, dark cannabis extract containing high concentrations of THC along with smaller amounts of CBD, other cannabinoids, and plant compounds like terpenes and waxes. People use it for everything from chronic pain and chemotherapy-related nausea to sleep trouble, and it gained its name and following largely because of cancer claims that remain unproven in humans. The gap between what preclinical research shows in lab dishes and what RSO can verifiably do for a person is wide, and understanding that gap is essential before deciding whether this oil has a place in your life.
What Makes RSO Different from Other Cannabis Oils
RSO is made by soaking cannabis flower in a hydrocarbon solvent (traditionally naphtha or isopropyl alcohol), then boiling off the solvent to leave behind a tarry, concentrated oil. Because the process strips nearly everything from the plant into the final product, RSO is considered a “full-spectrum” extract. That includes not just THC and CBD but also minor cannabinoids like CBN and CBG, along with chlorophyll, plant waxes, and whatever terpenes survive the heating steps.
The heating matters. RSO is decarboxylated during production, meaning the THC is already in its active form and does not need to be smoked or vaporized to produce effects. However, that same heat strips out a substantial share of the volatile terpene content. Research on cannabis extraction shows that the terpene beta-myrcene, for instance, drops from about 68% of the terpene profile in raw flower to roughly 15% in decarboxylated oil, and other terpenes like alpha-pinene follow a similar downward trend.1Journal of Pharmaceutical Research International. Determination of Terpenoid Profile in Dry Cannabis Flowers and Extracts Obtained from Different Cannabis Varietes RSO also carries plant-derived waxes, including long-chain alkanes in the C22 to C31 range, which are absent in more refined concentrates like distillates.2ACS Omega. Temperature Control Minimizes Wax-Derived Alkane Carryover in Hydrocarbon Cannabis Extraction Whether those waxes do anything beneficial is unclear; they mostly distinguish RSO’s thick consistency and dark color from the cleaner look of distillate or isolate products.
THC content in RSO typically falls between 60% and 90% by weight, making it one of the most potent oral cannabis products available. That potency is the source of both its perceived benefits and its most serious risks.
The Cancer Claims and What the Science Actually Shows
RSO’s fame rests largely on the story of Rick Simpson, a Canadian who said he applied homemade cannabis oil to basal cell carcinoma spots on his skin and that they disappeared. He subsequently promoted RSO as a cancer cure, and that narrative spread widely online. No controlled human trial has ever confirmed that RSO or any cannabis oil can cure cancer.
What does exist is a body of preclinical research, meaning experiments in cells and animals, showing that THC and CBD can interfere with cancer-cell growth under laboratory conditions. Cannabinoids have been shown to affect signaling pathways involved in cancer-cell proliferation and survival, and they can slow tumor growth in animal models.3PubMed Central. Anticancer mechanisms of cannabinoids One recent cell-culture study found that a CBD/THC mixture promoted apoptosis (programmed cell death) in breast cancer cell lines, including a particularly aggressive triple-negative type, through a mitochondrial pathway.4Scientific Reports. The molecular anti-metastatic potential of CBD and THC from Lebanese Cannabis via apoptosis induction and alterations in autophagy
These findings are real and worth following, but they do not translate to a treatment recommendation. Cells in a dish lack an immune system, a liver, and blood flow. Plenty of substances kill cancer cells in vitro but fail or even cause harm in living humans. Preclinical work on cannabinoids and skin cancer illustrates the complexity well: while some studies suggest antitumor effects on skin cancers, others have found that cannabinoids can act as pro-inflammatory agents in cell-culture models, potentially encouraging the opposite of what you want.5PubMed Central. Tetrahydrocannabinol and Skin Cancer: Analysis of YouTube Videos The honest summary is that cannabinoids interact with cancer biology in ways that are promising enough to keep studying, but no one should delay or replace conventional cancer treatment with RSO.
Palliative Use in Cancer Patients
Where cannabis products like RSO have more grounded clinical support is in managing the side effects of cancer and its treatment rather than the disease itself. Several studies support the use of cannabis for chemotherapy-induced nausea and cancer pain.6PubMed. Cannabis Use in Patients With Cancer: A Clinical Review Synthetic THC (dronabinol) has been FDA-approved for chemotherapy nausea since the 1980s, and RSO delivers a much higher and less standardized dose of the same active compound.
Appetite stimulation is another commonly reported benefit. Cancer patients dealing with wasting often use RSO specifically because its high THC content can trigger hunger. The flip side is that the doses involved bring significant psychoactive effects, so there is a practical tradeoff between stimulating appetite and being too impaired to function during the day.
Chronic Pain
Pain is probably the single most common reason people seek out RSO. The evidence here is more nuanced than many advocates suggest. A Cochrane systematic review on cannabis-based medicines for chronic nerve pain found that THC/CBD-balanced products may produce modest improvements in patient-reported global impressions of change, but the evidence for achieving a 50% or greater pain reduction was unclear and rated as very low certainty for THC-dominant and CBD-dominant medicines alike.7PubMed. Cannabis-based medicines for chronic neuropathic pain in adults
An earlier version of that same Cochrane review put some numbers on the picture: roughly 21% of people using cannabis-based medicines achieved at least 50% pain relief, compared with 17% on placebo, and about 39% achieved at least 30% relief versus 33% on placebo. The reviewers noted that the potential benefits might be outweighed by the potential harms.8PubMed Central. Cannabis‐based medicines for chronic neuropathic pain in adults That is not zero benefit, but it is far from the dramatic pain relief you might expect based on anecdotal claims. And RSO specifically has not been tested in these trials; most used standardized pharmaceutical products with known doses. The uncontrolled potency of homemade or dispensary RSO makes it harder to predict what you will get.
Seizure Disorders
One area where cannabinoids have earned genuinely impressive clinical results is in certain severe childhood epilepsy syndromes. A prospective trial of a CBD/THC cannabis oil in Dravet syndrome, one of the most treatment-resistant forms of epilepsy, found a median motor seizure reduction of about 71%, with 63% of patients achieving at least a 50% reduction in seizures. Quality of life improved and abnormal brain wave activity decreased.9PubMed Central. A prospective open-label trial of a CBD/THC cannabis oil in dravet syndrome The FDA-approved drug Epidiolex, a purified CBD product, came out of this line of research.
RSO is not Epidiolex. It contains far more THC and far less standardization. Some families of children with intractable epilepsy do use full-spectrum oils under medical supervision, but the THC content adds risks (especially cognitive and psychiatric effects in children) that a CBD-only product avoids. If seizure control is the goal, the regulated pharmaceutical route has a stronger evidence base and a clearer safety profile.
Sleep
Many RSO users report that it helps them fall asleep, and THC is well known for its sedating effects at higher doses. The research picture is more complicated than “it helps you sleep,” though. A randomized, placebo-controlled trial in people with insomnia found that a CBD/THC combination actually decreased total sleep time by about 25 minutes compared to placebo. It also significantly cut time spent in REM sleep and delayed REM onset by over an hour.10SLEEP. 0371 Acute effects of cannabinoids in insomnia disorder: a randomised, placebo-controlled trial using high-density EEG
That REM suppression is worth thinking about. REM sleep is important for memory consolidation and emotional processing. You might feel like you are sleeping more soundly on RSO because the sedation hits hard, but the underlying sleep architecture may be worse, not better. Long-term REM suppression from chronic use could have cognitive consequences, though this has not been studied specifically with RSO over extended periods.
How RSO Is Taken
RSO is most commonly swallowed or placed under the tongue. It can also be applied topically to skin, and some patients use rectal suppositories. Each route delivers cannabinoids differently.
When swallowed, THC passes through the liver before reaching the bloodstream. The liver converts a portion of THC into 11-hydroxy-THC, a metabolite that crosses the blood-brain barrier more readily and produces stronger psychoactive effects. During sustained oral dosing, this metabolite builds up steadily in the blood even as THC itself plateaus. After the last dose, THC can remain detectable in plasma above 1 microgram per liter for at least a day.11PubMed Central. Delta9-tetrahydrocannabinol (THC), 11-hydroxy-THC, and 11-nor-9-carboxy-THC plasma pharmacokinetics during and after continuous high-dose oral THC This lingering presence explains why people sometimes feel “off” well into the following day after a heavy RSO dose.
Rectal administration is an option for patients who cannot swallow, such as those with severe nausea or end-of-life conditions. A suppository formulation of a THC prodrug showed lower peak blood levels but roughly two and a half times the overall systemic exposure compared to an equivalent oral dose of dronabinol, meaning the body absorbs more total THC even though the peak hit is gentler.12Medical Cannabis and Cannabinoids. Pharmacokinetics and Tolerability of Δ9-THC-Hemisuccinate in a Suppository Formulation as an Alternative to Capsules for the Systemic Delivery of Δ9-THC Newer sublingual and suppository cannabis formulations have shown faster absorption and in some cases less variable uptake than traditional oil-based oral products.13PubMed. Comparative Pharmacokinetic Assessment of Innovative Sublingual, Rectal and Vaporizer Cannabis Products Versus Approved Cannabis Products in Healthy Volunteers
Topical use (applying RSO directly to skin) is popular among people targeting localized pain or skin lesions. THC and CBD do not readily penetrate the skin into the bloodstream, so topical application generally produces local effects without significant psychoactivity. That also means the systemic cancer-fighting claims made about topical RSO are poorly supported, since the cannabinoids are unlikely to reach deeper tissues in meaningful amounts.
Psychiatric Risks
The psychiatric risks of high-THC cannabis use are real and dose-dependent, and RSO sits at the extreme end of the potency scale. Research has found that people experiencing a first episode of psychosis were more likely to have used high-potency cannabis, used it more frequently, and used it for longer durations compared to healthy controls, consistent with the idea that THC itself is the ingredient increasing psychosis risk.14PubMed Central. High-potency cannabis and the risk of psychosis
Psychotic symptoms are not limited to people with pre-existing mental illness. Case reports have documented transient psychosis, including depersonalization, paranoia, and derealization, in otherwise healthy occasional cannabis users following oral administration.15PubMed Central. Two cases of “cannabis acute psychosis” following the administration of oral cannabis The oral route is particularly risky for overconsumption because effects take 30 to 90 minutes to appear, leading people to take more before the first dose has kicked in. A practical dosing guideline that appears in the medical literature suggests keeping total daily THC below 30 milligrams and combining it with CBD when possible to limit psychoactive effects and tolerance development.16PubMed. Practical considerations in medical cannabis administration and dosing For context, a rice-grain-sized dose of RSO, the amount often recommended as a starting point, can contain anywhere from 5 to 25 milligrams of THC depending on the product.
Cardiovascular Effects
THC affects the heart and blood vessels in ways that shift with dose and duration of use. A single dose typically increases heart rate and may raise blood pressure, while prolonged daily THC ingestion has been shown to produce heart rate slowing and blood pressure lowering in controlled settings.17PubMed. Cardiovascular effects of prolonged delta-9-tetrahydrocannabinol ingestion The literature identifies three major cardiovascular concerns with THC: a condition resembling peripheral artery inflammation sometimes called “cannabis arteritis,” cannabis-induced blood vessel spasms, and effects on platelet aggregation.18PubMed Central. The Cardiovascular Effects of Marijuana: Are the Potential Adverse Effects Worth the High?
If you have a heart condition, use RSO with caution and involve your doctor. The rapid heart rate increase from a single large oral dose could be dangerous for someone with arrhythmia or coronary artery disease, and the long-acting nature of oral THC means those effects persist for hours.
Cannabinoid Hyperemesis Syndrome
One of the stranger risks of regular high-dose cannabis use is cannabinoid hyperemesis syndrome, or CHS. Despite cannabis’s well-known anti-nausea properties, chronic heavy use can paradoxically trigger severe nausea, vomiting, and abdominal pain that cycles repeatedly until the person stops using cannabis entirely.19PubMed Central. Cannabinoid Hyperemesis Syndrome: A Rising Complication CHS has historically been underdiagnosed because both patients and clinicians assume cannabis should help nausea, not cause it. The hallmark symptom is compulsive hot showering or bathing, which temporarily relieves the discomfort through an unknown mechanism.
RSO users may be at particular risk for CHS given the high doses involved in common protocols. The “Rick Simpson Protocol,” which circulates informally online, escalates to a full gram of RSO per day over several weeks. At 60% to 90% THC, that amounts to 600 to 900 milligrams of THC daily, far above the threshold where CHS becomes a concern and vastly exceeding the 30-milligram ceiling mentioned in clinical guidance.
Drug Interactions
A risk that gets far too little attention in the RSO community is the potential for cannabinoids to interfere with other medications. Both THC and CBD inhibit certain liver enzymes responsible for metabolizing many common drugs. The enzyme most broadly affected is CYP2C9, which was inhibited by nearly all cannabinoids tested in one study at concentrations that could realistically be reached during regular use. The researchers specifically flagged that drugs metabolized by CYP2C9 with a narrow therapeutic index, where small changes in blood levels can cause toxicity, may be at risk for meaningful interactions.20PubMed. Cannabinoid Interactions with Cytochrome P450 Drug Metabolism: a Full-Spectrum Characterization Warfarin, the blood thinner, is metabolized by CYP2C9, and case reports of dangerously elevated warfarin levels in patients using cannabis products have been documented.
It is not just THC and CBD themselves. The metabolites your body creates after processing THC also inhibit multiple liver enzymes, including CYP2B6, CYP2C9, and CYP2D6.21Drug Metabolism and Disposition. Cannabinoid Metabolites as Inhibitors of Major Hepatic CYP450 Enzymes, with Implications for Cannabis-Drug Interactions Because oral THC and its metabolites linger in the body for well over a day after a dose, the window for interaction is wide. If you take prescription medications, especially blood thinners, anti-seizure drugs, certain antidepressants, or medications your pharmacist has described as having a “narrow therapeutic window,” this is not a theoretical concern.
Contamination and Quality Control
RSO is frequently made at home or sourced from unregulated producers, and contamination is a serious and well-documented problem across cannabis concentrates. A study that screened 57 cannabis concentrate samples found that over 80% were contaminated with residual solvents, pesticides, or both.22The Journal of Toxicological Sciences. Understanding dabs: contamination concerns of cannabis concentrates and cannabinoid transfer during the act of dabbing Home extraction with solvents like naphtha or isopropyl alcohol carries additional risks if the solvent is not fully purged, and consumer-grade solvents may contain impurities of their own.
Even in regulated markets, product quality is inconsistent. An analysis of 29 commercially available cannabinoid supplements found that only 18 were accurately labeled according to regulatory guidelines, with wide variation in actual cannabinoid concentrations.23PubMed Central. Cannabinoid, Terpene, and Heavy Metal Analysis of 29 Over-the-Counter Commercial Veterinary Hemp Supplements A clinical framework for evaluating cannabis product quality emphasizes that regulated products, those subject to independent testing and contamination limits, are meaningfully safer than unregulated ones, and that widespread standardization is still lacking.24PubMed Central. A Clinical Framework for Evaluating Cannabis Product Quality and Safety
If you decide to use RSO, buying from a licensed dispensary in a state with mandatory testing is the minimum bar for safety. Ask for a certificate of analysis showing cannabinoid content, residual solvent levels, pesticide screens, and heavy metal testing. If the seller cannot provide one, that tells you something. Home-produced RSO, regardless of how carefully someone follows an online tutorial, has no quality assurance at all.
How RSO Compares to Pharmaceutical Cannabis Products
Several standardized cannabis-derived drugs are now available by prescription in various countries. Dronabinol and nabilone are synthetic THC pills approved for chemotherapy nausea and AIDS-related wasting. Epidiolex is purified CBD approved for certain seizure disorders. Nabiximols (brand name Sativex in many markets) is a THC/CBD mouth spray used for multiple sclerosis spasticity in countries outside the United States.
These products exist in a different regulatory universe from RSO. Their doses are precisely measured, their purity is verified by manufacturing standards, and their effects have been studied in controlled trials. RSO advocates often argue that the full-spectrum nature of the oil provides an “entourage effect,” where the combination of cannabinoids and terpenes works better together than any single compound alone. That idea has some theoretical backing, but the evidence for it is largely preclinical, and the terpene loss during RSO production undermines the argument to some extent. The practical advantage of pharmaceutical products is consistency: you know what dose you are getting, and your doctor can adjust it based on response.
That said, cost and access push many patients toward RSO. Pharmaceutical cannabis products are expensive, often not covered by insurance, and in many places harder to obtain than dispensary or homemade oil. The choice between a well-studied, precisely dosed pharmaceutical and a highly variable full-spectrum extract often comes down to what a person can actually get their hands on and afford, which is a systemic problem more than a personal one.