What Is Rick Simpson Oil (RSO)? How It’s Used and How It’s Made

Last updated on September 10, 2026 · Originally published December 13, 2017

Rick Simpson Oil (RSO) is a potent, full-spectrum cannabis extract that has become one of the most widely used and talked-about products in medical cannabis. The oil takes its name from Rick Simpson, a Canadian cannabis activist who popularised it in the early 2000s after using a homemade cannabis oil to treat skin cancer lesions – though high-THC cannabis oil extracts had existed long before Simpson brought them to mainstream attention.

What made RSO distinctive wasn’t a new extraction technology. It was Simpson’s decision to share his protocol openly, distribute the oil free of charge, and document his experience treating thousands of patients – which turned a relatively obscure preparation into a fixture of medical cannabis culture worldwide.

What Makes RSO Different From Other Cannabis Extracts?

RSO is generally considered a full-spectrum cannabis extract because it retains a broad range of cannabinoids and many of the plant’s naturally occurring compounds. That said, the exact chemical profile varies depending on the extraction method and starting material – and some volatile terpenes may be lost during the alcohol evaporation process, meaning commercial RSO products can differ significantly from one another. This distinguishes it from isolates (pure CBD or pure THC) and from distillate-based products, which are refined down to an even narrower cannabinoid profile by design.

The extraction method also sets RSO apart. Where BHO uses butane as a solvent, RSO is traditionally made with an alcohol-based solvent – a process that strips the plant material of its chemical compounds and leaves behind a thick, dark, highly concentrated oil. The finished product is characteristically dense and sticky, with a dark brown or black color that comes from the full range of plant compounds being retained rather than filtered out. Which solvent, exactly, turns out to matter a great deal – more on that below.

How Strong Is RSO?

THC content in commercial RSO typically runs between 60 and 90%, making it one of the more potent extract formats available. Because RSO is extremely thick and sticky, it’s almost always packaged in oral syringes, which allow patients to dispense very small, accurate doses – a practical necessity given how concentrated the oil is.

How to Use Rick Simpson Oil

In the legal cannabis market, patients can generally find RSO at their local recreational or medical cannabis shop. Once they bring it home, however, many patients aren’t sure how to use it.

Simpson famously applied the oil directly to skin cancer lesions. While RSO is commonly used topically for various skin conditions, there is currently no high-quality clinical evidence demonstrating that topical RSO treats skin cancer. For those who need to take the medicine internally, they should ingest it. Dabbing RSO is not advised – the high residual plant material content and the alcohol extraction method make it unsuitable for the high-heat application that dabbing requires.

Starting dose: Because RSO is highly concentrated, starting low is important. Most clinicians and cannabis-experienced healthcare providers recommend beginning with a very small amount, once or twice a day. This allows the user to gauge the psychoactive effects before increasing the dose.

Titrating up: Any dose increases should be gradual and based on individual tolerance and response. Simpson’s original protocol called for doubling the dose every few days toward a target of 1 gram daily – an escalation pace that many patients find too aggressive, particularly those who are older, THC-naive, or sensitive to psychoactive effects. There is no clinical evidence that faster escalation produces better outcomes, and side effects from moving too quickly (disorientation, anxiety, excessive sedation) are common. A slower, more conservative approach – increasing dose weekly rather than every few days, and stopping once the desired therapeutic effect is achieved rather than chasing a fixed target – is likely safer and more tolerable for most people.

How to take it: RSO can be placed under the tongue or between the gums and the inside of the lip, where cannabinoids absorb into the bloodstream more directly than through digestion. It can also be mixed into food – though its bitter taste usually needs masking. Mixing it into something fatty (nut butter, coconut oil, avocado) can support absorption, since cannabinoids are fat-soluble.

Talk to a provider first: RSO at therapeutic doses involves significant THC quantities. THC and other cannabinoids can inhibit or compete for liver enzymes in the cytochrome P450 system, potentially altering how some medications are metabolized – including blood thinners, certain antidepressants, and some chemotherapy agents [4]. Anyone using RSO alongside other medications, or for a serious condition, should discuss it with a healthcare provider before starting.

Storing RSO

RSO should be stored in an airtight container, away from light and heat. A cool, dark drawer or the refrigerator works well for longer-term storage. The thick, sticky consistency makes it harder to work with when cold, so allowing it to come to room temperature before dosing is practical. Stored correctly, RSO holds up well over several months without significant loss of potency. The same principles that protect flower – cool, dark, airtight – apply here, and the research behind them is covered in our guide to storing cannabis.

How RSO Is Made – and Why the Solvent Matters

The process behind RSO is conceptually simple. Plant material is washed in a solvent that pulls out the cannabinoids. The liquid is strained, and the solvent is evaporated off with gentle heat, leaving the thick, dark oil behind.

One step is easy to get wrong here: decarboxylation. The evaporation heat alone does not reliably convert THCA into active THC – while alcohol remains, evaporative cooling caps the mixture near the solvent’s boiling point, well below dependable decarb conditions. The 2013 analysis found that only deliberate high-temperature treatment achieved complete decarboxylation; milder processing did not [2].

In practice, that means decarbing on purpose: either the flower before extraction, or the finished oil afterward with continued gentle heat. That deliberate step is why RSO works orally when raw flower does not – and skipping it is why some homemade batches disappoint.

Beyond that, what separates one RSO from another is almost entirely the solvent, and the care taken removing it.

The naphtha problem

Simpson’s original method specifies naphtha or isopropyl alcohol. The claim that travels with it – that the solvent “all evaporates” – is false.

Naphtha is not one chemical. It is a variable mixture of petroleum hydrocarbons, and what is sold under that name ranges in quality all the way down to camping fuel. When researchers chemically analyzed Simpson-style oils in 2013, the extracts made with naphtha and petroleum ether still contained significant petroleum-hydrocarbon residues after evaporation [2,3].

Those residues are exactly what the residual-solvent panel on a laboratory COA screens for – the same testing category our contaminant testing pillar covers. For a patient consuming grams of concentrate daily, that is a medical issue, not a technicality.

Not all alcohols are equal

Isopropyl alcohol and food-grade ethanol are not interchangeable, either. Both evaporate readily – but food-grade ethanol is the only common home solvent produced and regulated for human consumption. Technical-grade isopropyl is not. And no solvent leaves the finished oil entirely.

The fire risk

Evaporating a large volume of alcohol fills the surrounding air with flammable vapor. Doing that indoors, over a heat source, is the same physics that produces home-extraction explosions.

We describe the process here so it can be understood – deliberately not as instructions. This is not a recipe.

If you make it anyway

• Food-grade ethanol only – never naphtha, never technical-grade isopropyl
• Decarb deliberately – the flower before extraction, or the oil after – rather than assuming the evaporation did it
• All evaporation outdoors, with ventilation, away from every flame and spark source – or better, in a closed-loop recovery unit, which exists at home scale and keeps the vapor out of the air entirely
• Never leave the evaporation unattended
• Keep the batch small
• If you have any access to a lab, test the finished oil – the residual-solvent panel is the number that matters

What licensed producers do differently

Commercial RSO is where the homemade original has genuinely been improved on. Licensed producers extract with cold ethanol in closed-loop systems that recover the solvent instead of releasing it as vapor – and closed-loop recovery units exist at home scale too, which removes most of the open-vapor fire risk in one purchase. What home production cannot replicate is the other half: every licensed batch is tested.

A dispensary RSO comes with a COA whose residual-solvent line answers, with numbers, the exact question this section raises. If you buy rather than make, that line item is the one to read.

Does RSO Treat Cancer?

This is the question at the heart of RSO’s reputation, and it deserves a direct answer: the evidence that RSO treats cancer in humans is currently limited to anecdotal reports and case studies. The preclinical research on cannabinoids and cancer cells is genuinely promising [1] – but promising in a petri dish or in mice is a long way from proven in humans. For a full look at what the research actually shows on RSO and cancer, including both the supporting studies and the evidence that complicates the picture, see our companion article: Does Rick Simpson Oil Actually Treat Cancer? What the Research Shows.

References

1. Munson AE, Harris LS, Friedman MA, Dewey WL, Carchman RA. Antineoplastic activity of cannabinoids. Journal of the National Cancer Institute. 1975;55(3):597-602. doi:10.1093/jnci/55.3.597
2. Romano L, Hazekamp A. Cannabis oil: chemical evaluation of an upcoming cannabis-based medicine. Cannabinoids. 2013.
3. Lazarjani MP, et al. Processing and extraction methods of medicinal cannabis: a narrative review. Journal of Cannabis Research. 2021;3:32. https://jcannabisresearch.biomedcentral.com/articles/10.1186/s42238-021-00087-9
4. Zendulka O, Dovrtělová G, Nosková K, Turjap M, Šulcová A, Hanuš L, Juřica J. Cannabinoids and Cytochrome P450 Interactions. Current Drug Metabolism. 2016;17(3):206-226. doi:10.2174/1389200217666151210142051

Originally published December 2017. Updated July 2026 (clinical guidance) and September 2026 (how it’s made, solvent safety, references). Reviewed by Nani Frenkel, chief editor.

RSO is one of several cannabis extracts covered in T&T’s extraction series. For a broader look at how RSO compares to BHO and other extracts, see our guide to cannabis extraction methods.