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When you should worry about leftover solvents in cannabis oil

January 29, 2020
cannabis concentrates
Many cannabis producers have moved beyond using solvent extractions to isolate cannabinoids and other desirable compounds from cannabis plants. However, there are still plenty of concentrate products available that involve the use of hydrocarbons—such as butane and propane—ethanol, or carbon dioxide to pull THC, CBD, terpenes, and more from raw cannabis plants.

While efforts are made to remove these solvents, it’s likely that some amount will end up in the final product. In regulated markets, there are specified levels of solvents that are allowed in products sold or prescribed to consumers.

But when it comes to products that are not regulated, such as those sold illicitly, it can be difficult to know how much of a solvent remains. That’s why it’s always important to get your cannabis products from a legal, licensed store.

When consumed at high levels, these solvents could pose health risks, some of which aren’t entirely established. In this article we’ll look at the regulations surrounding residual solvents and the risks these substances might pose to human health as a result of overconsumption.


What are cannabis concentrates, oils, and extracts?

Restrictions on solvent levels

Knowing that the presence of some residual solvents in cannabis products is inevitable, relevant authorities impose limits on the levels allowed for each type of solvent.

Solvents are classified in three divisions: Class 1, 2, and 3. Class 3 solvents have low toxic potential and are the only ones recommended for use in the production of cannabis extracts. However, it’s possible that some Class 1 and 2 solvents can end up in final products, often as contaminants of Class 3 solvents. For example, benzene, toluene, and xylenes (known collectively as BTX) are found in natural gas, from which butane is sourced.

This explains why you’ll find some pretty harmful substances on residual solvent lists. For example, in Colorado, benzene, a Class 1 solvent, is allowed at a level of up to two parts per million (ppm). 

We discuss state-by-state regulations for residual solvents in a separate article, but as an example, here are acceptable levels for Colorado:

Acceptable levels of residual solvents in Colorado

SubstanceAcceptable limits per gram
Butanes<5,000 ppm
Heptanes<5,000 ppm
Benzene<2 ppm
Toluene<890 ppm
Hexane<290 ppm
Total Xylenes<1 ppm

Canada, where cannabis products were legalized across the country in 2018, has its own set of regulations.

Health implications of ingesting common solvents

The main solvents used in cannabis extraction are carbon dioxide, butane, and ethanol. When it comes to consumption, extracts are most often vaporized, via a vape pen or dabbing, but they can also be incorporated into edibles. Less commonly, extracts are smoked, for example, by topping a bowl with wax or dipping a joint in concentrate. 

While residual carbon dioxide is not a concern, excess butane or ethanol could pose health risks, depending on levels and method of consumption. 


Butane offers a relatively simple and inexpensive method to extract a large percentage of THC and other desirable compounds from cannabis plants. But it has been the subject of much controversy when it comes to what is considered a safe amount. Some naysayers argue that long-term consumption of butane by ingestion or vaporization has not been studied widely enough to confidently say it’s safe at any level.

Regulators appear to disagree and in many regions, butane is allowed at the seemingly high level of 5,000 ppm. However, illegal products could contain much higher levels.


Leafly Investigation: How Much Butane in BHO Is Too Much?

So what harm can it do? According to studies, at high enough levels, butane inhalation can cause cardiac damage and organ failure, among other serious negative effects. While these risks are associated with direct inhalation of the solvent rather than practices such as dabbing, the latter may be harmful to health.

A 2019 study investigating an 18-year-old’s lung injury that resulted from frequent and prolonged inhalation of butane hash oil found: “There is a likely probability that a high level of inhaled butane also contributed to her symptoms.” 

It should be noted that in this case, the patient confirmed that the butane hash oil was purchased illegally. This indicates that the product contained an unknown level of butane which could have been well above what should be allowed in a regulated product.


In California, the maximum level of ethanol allowed is 1,000 ppm for medical cannabis goods meant for inhalation and 5,000 ppm for other medical cannabis-infused goods. Ingesting ethanol in these small amounts is unlikely to cause harm, even over a prolonged period.

However, according to this 2018 report (involving multiple studies conducted on animal or human subjects), ethanol inhalation could be more risky, potentially causing cravings, tolerance, and dependence. That said, studies tend to examine levels of ethanol exposure far higher than you would ever find in vape oil.


Cannabis Testing Explained: What’s in Your Cannabis?

Other solvents

Some other potentially harmful solvents end up in cannabis products because they are contaminants of the main Class 3 solvents used in extraction or because they are used to clean equipment used in the production process. 

Here are a few that may find their way into a final product:

  • Benzene: This is a known carcinogen that affects bone marrow. It is allowed, albeit at very low levels, in some cannabis products.
  • Xylenes: In vaporized form, xylenes can cause depression of the central nervous system. Depending on the level of exposure of these Class 2 solvents, symptoms can include nausea, headache, dizziness, and vomiting, among other symptoms.
  • Hexane: This Class 2 solvent can have similar effects as xylenes on the central nervous system if inhaled at high enough levels.

How to decide if a cannabis product is safe

To avoid risks associated with solvents, one option is to stick with solventless extracts such as rosin and bubble hash. But if you do go with a solvent-extracted product, the only real way to tell if it’s safe to consume is to purchase a legal, licensed, regulated product.

Regulated producers use high-quality solvents that minimize the risk of contaminants like benzene and xylenes ending up in your product. Plus, they use proper equipment to remove solvents post-processing. Finally, products are tested using rigorous methods such as headspace analysis and meet standards set by state regulators.  

If you’re unsure what to look for when purchasing cannabis products, check out our state-by-state guide to cannabis packaging and labeling laws. If you’re purchasing north of the border, Canada has its own packaging and labeling guide.

Aimee O'Driscoll's Bio Image

Aimee O'Driscoll

Aimee is a freelance writer and editor based outside Toronto. She holds a degree in Medicinal Chemistry and was a chemist for a multinational cosmetics company for almost ten years. Aimee has a passion for educating readers by breaking down complex science and technology topics.

View Aimee O'Driscoll's articles

  • Greg Maxim

    Or you don’t use any of those garbage chemicals to extract and instead use dimethyl ether in brands like pure 322 or mz12x from the UK. This is a completely natural and organic solvent that requires little to no vaccuum purging time. Fuck butane it’s dirty trash. Co2 makes it taste like shit. Heptane makes it catch fire.

  • Don Jumpsuit

    Really starting to understand why LEAFLY just fired a bunch of people. Butane is a propellant in String Cheese, it is the propellent in prescription based medical inhalers, and it is present at 10% in winter gasoline. Basically we are ingesting butane through inhalation constantly.

    Lastly, and this should be obvious. Stating something is “potentially dangerous” by using ONE EXAMPLE is about has dangerous and baseless as a claim can get. But obviously this crude form of publication is not above trying to get clicks or comments so congrats to you!

    • DEAD P1XL

      I think you’re confused. Spray cheese uses Nitrogen or Nitrous Oxide as a propellant. Inhalers use hydrofluoroalkane. Nothing consumed by humans directly like this is using butane as a pressure agent. For starters, butane liquifies at a very low pressure.

  • Reefer Rising™

    Give this story a C-. Headline an F. Please do better.

  • Randallpiz

    Butane killed my mother.


    This is why you use supercritical CO2 extraction. None of the chemical risks of hydrocarbon solvents, inexpensive, and very effective. All the oils I’ve seen at the dispensaries out here in Mass are made this way.

    • TincExtrax

      Just an FYI. The risks with CO2 sit within post processing and there are a lot of steps depending upon desired results. Every single CO2 Vape pen has/needs additives in order to consume. I live East Coast but train/visit in Portland Oregon and LA many times a year. I just returned 3weeks ago from visiting both. Hydrocarbon extracts “Live Resin, Live Sauce carts, etc…” prices are through the roof.
      CO2 falling fast as the facts come to light. It’s a cheaper version of the real..
      I love MASS… and East coast, I’m born and bread… but politics is why only CO2 is used and lack of new acquired knowledge by the extractors. Last but not least, the big one. They already spent a boatload on their overpriced CO2 equipment.

      I have 6yrs extracting. Have hydrocarbon and CO2 extracted. The amount of post processing for “Clean” CO2 products should steer most away if not the taste. (OH the taste…yuk)
      CO2 canna products must be reengineered. CO2 is compressed into a “Solvent” YES a Solvent at (1500 – 5000 psi).
      Light Hydrocarbon Extracted canna products – no need to add anything… only a specific temp and vacuum purge times dependent on final desired product and produce a true/real rep of original input. Reflects best what nature intended.
      With proper purging No process beats Light Hydro.
      Flavors, smells, effects etc…

      ROSIN is only non-solvent process but then it even needs a thinner for vape pens.

      CO2 Companies are now mixing Hydrocarbon extracted Live Resins with their CO2 products in order to compete with flavor and effect.

      I have spoken with as many bud tenders as possible from several dispensaries over the yrs. The common consensus was CO2 has a “hollow high” , fast up quick to down. whereas Live resin and or sauce carts are full bodied true representation of the strain and the effects last longer.
      West coast Live Resin Carts almost double the price of the best CO2?
      I started with Hydrocarbons then went the CO2 route as many due because cleaner is better for me… I quickly returned to the latter after I learned the truth about both processes.

      The public only knows what the big money companies want ya to know. Eventually EastCoast will catch up… Actually probably not.

      Best for everyone is to visit Oregon and LA and don’t be afraid to talk and ask. Visit many dispensaries. They are most so willing to share the knowledge the truth.

      For Medical, me personally… the less post processing needed for clean end results the better.
      Happy to share and answer any questions.

  • rainbowwildliferescue

    “That’s why it’s always important to get your cannabis products from a legal, licensed store.” <– great advice, unless you live in Texas :(.

  • Howard Paris

    The solvent restrictions appear to be extremely conservative if one compares them to the limits listed for the ‘Permissible Exposure LImit’ (PEL – 8 hour day) or ‘Short Term Exposure LImit’ (STEL – 15 minutes) listed by Cal OSHA or NIOSH. For Cal/OSHA, they are Acetone: 750 ppm STEL, Ethanol 1000 ppm PEL, Butane 800 ppm PEL, n-Hexane 50 ppm PEL, and Benzene 5 ppm STEL, 1ppm PEL. What is needed is an easily performed headspace analysis of vaporized extract to see what level of contamination actually generates an inhalable molecule. I suspect that the actual concentration generated from a realistic ‘hit’ will be one or even several orders of magnitude lower than the comparable established OSHA or hygiene-based limits. The industry could quickly dispense with or at least reduce the analytical burden with a minimal amount of real-world testing on metals, solvents, pesticides and microbiological contaminants. These overreaching restrictions are likely to be a matter of regulators taking their cue from analytical labs seeking more needless testing.

  • Lydia McFadden

    How to sensibly buy LEGAL CBD oil? Because I got a letter saying customs have confiscated my package two times already and I’m pissed.