Limonene: The citrus-scented terpene in medical cannabis

What is limonene, and where can it be found in nature?

Limonene (or d-limonene) is a mono-terpene that is found all throughout the plant kingdom. It comes in high concentrations, unsurprisingly, in citrus fruits like lemons, limes, oranges, and grapefruits. It also shows up in herbs like rosemary and peppermint, as well as other plants such as juniper, ginger, turmeric, and eucalyptus.

There are over 20,000 terpenes naturally produced, but only about 400 of them can be found in cannabis plants, and limonene is one of the most prevalent.

Cannabis flowers (and some of the smaller leaves) are covered in crystal-like 'trichomes'. These resinous glands are where cannabinoids like THC and CBD are produced and also where you will find the terpenes.

Not all lemony-smelling cannabis strains actually produce high levels of limonene. The only way you can be 100 percent certain is through lab testing, which all Releaf medical cannabis products undergo.

How much limonene do cannabis plants actually produce?

While the percentages for CBD and THC can range between 0% and 30%, terpenes come in much lower concentrations. Limonene will usually only make up about 2% of the dry weight, but this is more than enough to have a noticeable effect on the aroma and effects of a particular strain.

What role does d-limonene play in medical cannabis?

Terpenes play a few key roles for cannabis plants. They can help the plant protect itself from invaders while inviting beneficial pollinators. They also provide much of the smell and flavour we associate with different plants.

But, most importantly for medical cannabis patients, terpenes work together with cannabinoids to enhance their effects. 

This 'entourage effect' is an important function for medical cannabis patients to understand. In short, the 'entourage effect' refers to the synergistic relationship between certain cannabis compounds and how, when taken together, they can produce more significant effects than if taken separately.

Limonene has actually been quite extensively studied, but more research is needed to understand the therapeutic potential of d-limonene in medical cannabis fully.

So far, research has shown limonene can:

Relieve pain

Medical cannabis is often prescribed to people who don't respond well to conventional pain medication. THC has been proven to offer great analgesic relief, but the inclusion of limonene may also play a role.

By stimulating the TRPA1 receptor, limonene can reduce the sensitivity of nerves that detect pain signals. It has also been shown to help with nerve regeneration, which may be beneficial for patients suffering from neuropathic pain.

Provide anti-anxiety effects

There are a few studies looking into the effectiveness of limonene for anxiety, with most showing very promising results. One study that focused on limonene in conjunction with THC found that "D-limonene selectively attenuated THC-induced anxiogenic effects, suggesting this terpenoid could increase the therapeutic index of THC".

A little hard to decipher, but what this is essentially saying is that limonene may offset some of the potential anxiety-inducing effects of THC, making it a useful compound for medical cannabis patients who may experience anxiety as a side effect.

Another study showed that limonene inhibits anxiety-related behaviour by interacting with our creasing dopamine levels, which is another promising sign for those looking to use cannabis-based options as a treatment for anxiety.

Reduce inflammation

Inflammation is a vital part of the human immune system, but when it spirals out of control, it can cause all sorts of health problems. There have been a bunch of studies looking at how limonene may help a range of inflammatory conditions, with mostly very positive results.

• We have this systematic review looking at respiratory inflammation, which found that "Limonene has effective anti-inflammatory activity in both preventing and controlling respiratory system injuries."
• This study focused on limonene's effect on ulcerative colitis, an inflammatory bowel disease, and found that Limonene had a beneficial effect on ulcerative colitis in mice through a range of pathways.
• Another looked at limonene's effects compared to Ibuprofen and other pharmaceuticals, finding that "D-limonene probably exerts anti-inflammatory effects through the suppression of TNF-α, IL-1β, COX-2, and iNOS and NO, PGE2 production."

In short, limonene definitely looks to be a potent anti-inflammatory and may offer patients suffering from all types of chronic inflammation a natural remedy with little to no side effects.

Reduce tumour growth

Medical cannabis will not cure cancer, but there is very early research indicating that limonene may help slow the progression of many cancer types.

One systematic review, which looked at 8 separate studies, found that "when administered topically, through diet, or via oral gavage, limonene has shown the ability to suppress tumour growth by reducing tumour size, number, weight, and multiplicities in a dose-dependent manner"

More in-depth clinical research and trials are needed before any concrete claims can be made regarding limonene's efficacy as a cancer treatment, but the preliminary results are promising.

Combat acid reflux and heartburn

Limonene is lighter than water, so when it is taken orally, researchers believe it floats on the surface of gastric juices and lines the oesophagus, making it easier for food to pass through and reducing acid reflux symptoms. 

While more research is needed to fully understand how limonene works so effectively as a stomach-soothing agent, the amount of anecdotal evidence is pretty convincing.

Is limonene safe?

It sure is. Limonene has been shown repeatedly to be totally safe for human consumption.

Can humans be allergic to limonene?

Yes, there is a chance that you may have a limonene allergy. But, it is a very rare occurrence. In fact, limonene is actually used in allergy testing as a positive control for skin reactions due to its generally low chance of causing allergic reactions.

How is limonene extracted from medical cannabis?

Most medical cannabis extracts are made through CO2 supercritical extraction, using high-tech machines to extract individual compounds from the plant material.

But you don't necessarily need to take an extract. Many UK medical cannabis strains, like Releaf Tangerine Boost, Releaf Strawberry Sorbet, Zookies, and Fiji Sunset come with elevated levels of limonene.

How is limonene used in skincare and other industries?

Limonene is a very common addition to skincare products. In cosmetics, it is often used as a fragrance and also for its antibacterial properties. It's also added to cleaning products for the same reasons, boosting the scent and killing the bacteria.

FAQs

What does limonene do, and what are its effects?

That depends on its application, but in medical cannabis, limonene has been shown to be a potent anti-inflammatory, anti-bacterial, analgesic, antianxiety, and potential anti-tumour compound. It has also been shown to help with gastro issues.

What foods contain limonene, and what is it used for in the culinary world?

Most citrus fruits, as well as certain herbs and other edible plants, have high levels of limonene. Limonene is all about that sharp sourness. It's a common flavouring in drinks, sweets, and baked goods and is used to add extra zest to food or drink.

What is the relationship between limonene and linalool in terms of therapeutic effects?

Linalool is another common cannabis terpene, and it shares many similar therapeutic effects with limonene, such as anti-anxiety and analgesic properties. In terms of their relationship, linalool may enhance the effects of limonene when taken in combination, thanks to their matching therapeutic offerings and the entourage effect.

How can I be sure that my prescription contains limonene?

Always ask your prescribing specialist or pharmacist for a Certificate of Analysis from the manufacturer. This document lists terpene levels and other important information.

If you are taking an extract or oil, you should check to see that it is either full-spectrum or broad-spectrum. These oils contain not just one isolated compound but the full spectrum (or close to) of terpenes and other plant compounds, including limonene.

The wrap-up

Anti-pain, anti-inflammation, anti-bacterial, anti-anxiety, and may potentially help reduce tumour size and progression - limonene is one powerful terpene. When taken in conjunction with cannabinoids and other terpenes, it may offer even more benefits thanks to the entourage effect.

From skincare to stomach woes, pain (both physical and emotional), and potential tumour mitigation, limonene is a versatile and natural complementary treatment option with few side effects. To learn more about cannabis-based therapy options, feel free to check out our blog and education sections, both filled to the brim with evidence-based information and expert advice.

And, as always, please consult with a cannabis medicine specialist before making any changes to your treatment regimen.