Rick Simpson Oil (RSO) is a full extract cannabis oil made from the flowers of the cannabis plant. It is named after its Canadian creator, Rick Simpson, who used it to treat his tinnitus and later claimed to have cured three small spots of skin cancer with regular application of his special cannabis oil. RSO is made by submerging marijuana buds in a solvent, such as pure light naphtha, and then boiling off the solvent leaving behind the oil. The end product is a high potency oil often dark in color with a thick consistency. RSO is typically considered more potent than other cannabis oils, but it should be used with caution and at a low dose.

RSO can be consumed orally, applied topically, or smoked. It is a full-spectrum extract, meaning it still contains all the cannabinoids of the plant, including THC. RSO has been sold as an unproven treatment for cancer, but as of 2022, no such properties are known. However, some early research suggests that some chemicals in marijuana have future potential as a cancer treatment. RSO has also been claimed to have healing benefits for other conditions such as pain, nausea, loss of appetite, and multiple sclerosis.

RSO is not a branded product, and there is no one "Rick Simpson Oil" for sale. However, Rick Simpson explains how to make his namesake oil on his website, but he does not sell a version of the oil for profit. RSO is illegal to buy in many places because it contains high levels of THC. In states that have legalized marijuana, RSO can be found at cannabis dispensaries.