When it comes to medical cannabis, there are so many different compounds that have been found to have positive attributes, that it’s hard to count them all. From cannabinoids like THC and CBD, to the power of terpenes like limonene.
In order to define limonene, it’s important to understand what a terpene is. A terpene is a hydrocarbon found mainly in essential oils, balms, and resins. While cannabis flowers are known for having an abundance of terpenes, including limonene, they can actually be found all over the place in many different plants, and it is often these terpenes that help determine the scent or flavor of a plant.
When you think of the sweet smelling plant lavender – that’s the terpene linalool you’re smelling, or the strong scent of pine, well that comes from a combination of several terpenes, primarily pinene and limonene. And indeed, many of the smells and tastes associated with the cannabis plant are also due to the make-up of terpenes.
All that said, limonene is a terpene that is found in relative abundance in cannabis plants as well as in many other places. In fact, if you couldn’t guess it from the name, lemons contain large quantities of limonene giving them their aromatic citrus smell and flavor. Citrus fruits contain what is called D-limonene.
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Are there health benefits to limonene?
One of the main points of interest with limonene is its potential as an anti-tumor agent. In this 2018 systematic review of limonene and its metabolites, it was stated “Limonene and its metabolites have demonstrated numerous biochemical effects as chemotherapeutic agents. They are recognized as anticancer agents owing to their ability to induce apoptosis by up-regulating of pro-apoptotic factors and down-regulating anti-apoptotic factors.”
The same review went on to state later that though limonene and its metabolites have important pharmacological abilities that are well-known, their benefits are often limited by low bioavailability, low general distribution in tissues, and low plasma and metabolic stability. The review proposed using more effective drug delivery systems, nanoformulations, and a prodrug approach to improve these features.
When it comes to cannabis, it has already become common practice to isolate different compounds in order to make higher potency formulations, particularly of compounds that only exist in small amounts, like CBD, CBN, or delta-8 THC. Terpenes as well can be isolated and used in greater strengths than are found in nature.
What about stress and anxiety?
Stress and anxiety are another issue for which limonene may offer a useful medicinal response. In 2014 a study was done that investigated rats that were put under non-pathological stress and then injected with either limonene, or one of its metabolites (POH), perillyl alcohol. Tests were then performed afterwards on the rats at different time intervals.
It concluded, “These studies show that d-limonene exerts, through its metabolite POH, a significant anti-stress action measurable by behavioral and physiologic parameters under the influence of the nervous system. In addition to its anti-inflammatory effects, a beneficial role as an anti-stress substance could thus be claimed for d-limonene used as a dietary supplement.”
Even earlier than that in 2012, an animal study came out, the purpose of which was “to determine the acute toxicity and anxiolytic-like effects of a mixture of cis and trans of (+)-limonene epoxide in animal models of anxiety.” It suggested, in the end, “that acute administration of the (+)-limonene epoxide exerts an anxiolytic-like effect on mice, and it could serve as a new approach for the treatment anxiety, since it practically does not produce toxic effects.”
Why else is it important?
When looking at medicinal cannabis, most products are either made directly from the plant, like an oil extraction, edible, tincture, or the plant itself. Or, produced from isolated compounds of the plant that are amplified and taken alone. When taken alone, a compound can produce a lot of great effects. Just look at everything coming out about CBD – cannabidiol – and how that one compound has been shown to do a lot of good, from helping with anxiety and stress, to aiding in spastic disorders, to possible anti-cancer benefits, to a probable treatment for neurodegenerative diseases.
However, sometimes it’s the parts of the plant working in conjunction that produces the greatest effect, and this entourage effect – or synergistic effect, can’t be achieved when isolating and removing one component part, although it can be made by putting the correct components together outside of the actual plant. When looking at the entourage effect, different terpenes like limonene, are made stronger themselves, while also contributing to the strength of the other compounds in the plant.
The idea of drug synergism is that the interaction between component parts of something creates a greater total effect than the individual parts working alone. In this way, by simply being a part of the cannabis plant, limonene helps increase the power of the total plant.
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How extraction of terpenes works
Terpenes like limonene show up in only very small quantities in cannabis plants, even those that are considered limonene-rich flowers. In order to study them, or create more concentrated medications using them, they must be extracted from the plant. When extracting terpenes, it should be remembered that they’re delicate and too much heat is enough to render them useless. While older extraction methods lost a lot of terpenes or opened them up to contamination, there is a growing business for extraction these days, and different ways to do it have been established.
- Without using solvents: Steam distillation (putting plant matter above boiling water so the terpenes will be carried out with the stream to a condensation cup) and hydrodistillation (putting plant matter directly into boiling water).
- With solvents: Done with the use of hydrocarbons or gases like butane, nitrogen, CO2, and ethanol. These require lower boiling points, and use vacuums to reduce heat and prevent the degradation of compounds.
- Mechanical extractions: These methods use heat and pressure to separate the terpene liquids from the plant. The issue with these techniques is that they are less complete and do not fully isolate the terpenes leaving some amount of cannabinoids left behind as well.
Where to find limonene-rich flowers
All cannabis flowers have a different mix of terpenes and there are several different strains that are known for having high levels of limonene. The amount varies between different kinds of strains, and even between different plants in a batch. So just because the following are listed, it doesn’t mean that buying them will ensure a high level of limonene. Having said that, the below strains are some of the current best bets (according to Leafly) for finding high levels of limonene in cannabis flowers:
- Banana OG
- Berry White
- Black Cherry Soda
- Purple Hindu Kush
- Quantum Kush
- Strawberry Banana
- Tahoe OG
- Wedding Cake
- White Fire OG
As more is learned about the cannabis plant and all its component parts, and as better techniques come out for the isolation of molecules and production of products, better medications can be made by isolating and concentrating compounds for specific effects. This includes using cannabinoids, terpenes, and flavonoids too.
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