What is Full Spectrum Oil (FSO/RSO)?

Full Spectrum Oil (FSO) goes by many names: RSO, FECO, FSCO. Whatever you call it, FSO is somewhat of an anomaly in the cannabis industry. It’s frequently recommended by cannabis-savvy healthcare practitioners for its potential therapeutic benefits, yet it remains relatively rare to find on the market.

In this article, we’ll break down what FSO is, its history, how it’s made, and how people use it.

A Brief History: Rick Simpson and RSO

The term “RSO” comes from Rick Simpson, a Canadian who turned to cannabis after a head injury and later used it while treating skin cancer. Based on his positive experiences, Simpson developed a raw cannabis extract using solvents such as ether, naphtha, and 99% isopropyl alcohol.

He applied the concentrate directly to skin lesions and attributed his recovery to the extract. Motivated by his results, Simpson began publicly sharing his story and providing free instructions on how to make the oil at home. Over time, syringe-filled raw cannabis extracts became widely known as “Rick Simpson Oil” or RSO.

As legalization spread and commercial cannabis markets developed, the industry sought more universal terminology. That’s where names like FSO (Full Spectrum Oil) , FECO (Full Extract Cannabis Oil) , and FSCO (Full Spectrum Cannabis Oil) entered the picture.

(For more on Rick Simpson’s journey, you can visit his official website here .)

How Full Spectrum Oil is Made

Most FSO products today — including Proof’s FSO — are made using ethanol extraction. Ethanol is considered food-grade, “Generally Recognized As Safe” (GRAS), and is classified as a non-volatile extraction method under California regulations.

The process step by step:

1. Soak – Cannabis plant matter is soaked in ethanol.

2. Infuse – Cannabinoids, terpenes, pigments, lipids, and other plant compounds dissolve into the ethanol.

3. Strain – The plant matter is removed from the solution.

4. Evaporate – Ethanol is evaporated, leaving behind a thick, dark amber concentrate (similar in texture to molasses).

This concentrate may or may not undergo decarboxylation , the “activation” step that converts THCA (non-psychoactive) into THC (psychoactive). Proof’s FSO is fully activated.

Finally, the oil is typically packaged in a needleless syringe, which makes it easier to measure and dispense.

How to Use Full Spectrum Oil

Rick Simpson originally used cannabis oil topically, but today FSO can be:

• Ingested directly

• Mixed into food or beverages

• Applied in pre-portioned doses

Because FSO is thick, sticky, and strongly flavored, it’s not always the most user-friendly product for recreational consumers. Its appeal lies more in therapeutic and medicinal use.

Tips and Tricks:

Dispense Easier

Some batches, especially those with higher amounts of CBD in them, can harden and become difficult to dispense. We recommend soaking the syringe in hot water for a minute or two so the FSO can loosen up and flow easier.

Freezer Dots

For easier dosing, try dispensing small dots (0.05–0.1 ml) of FSO onto wax paper and freezing them. Once hardened, these can be taken like a tablet.

As with all cannabis products, start with a low dose and increase gradually.