As discussed in a previous article, Cannabis Terpenes and Their Benefits – Caryophyllene, Geraniol and Humulene, terpenes form a large group of phytochemicals, responsible for the organoleptic (aroma and flavour) characteristics of different Cannabis sativa L., strains under human domestication. Terpenes are secondary metabolites, fragrant oils secreted in trichomes (cannabis resin glands) alongside cannabinoids like tetrahydrocannabinol (THC) and cannabidiol (CBD). Part terpenoid, part phenol, both types of compounds are biosynthesised in the glandular trichomes of the leaves and flowers of the cannabis plant. Terpenes not only dictate the smell of cannabis and other plants, they also modify their effects.
Terpenes are very volatile, delicate molecules, easily destroyed by heat and oxidation. Popular cannabis concentrates, like BHO and CO2 oil, are mostly void of terpenes. One extraction method called live resin preserves the terpene profile of cannabis plants. This process involves cryogenically freezing plants immediately after harvest and then using a laboratory extraction process to remove and isolate a more accurate representation of a particular plant’s mix of cannabinoids and terpenes. There are about ten primary and twenty secondary terpenes that occur naturally in significant concentrations. D-limonene (limonene) as its name implies, provides an aroma of citrus and is found not only in cannabis, but also oranges, grapefruits, lemons, limes and some other herbaceous plants.
If you’ve ever wondered what gives cannabis strains like Super Lemon Haze, Chernobyl and Tangie that sweet citrus aroma, it’s limonene. Some strains tend to express higher levels of this terpene and often it’s the lemon scent that gives it away. Whereas THC levels typically make up 10-20% of a cannabis flower’s biomass, limonene occurs in trace amounts, generally none at all to 1-2%. Some strains exhibit higher levels than others but these levels can vary widely. One Jack Herer may test for high levels of limonene while another will demonstrate a disappointing lack thereof. The only way to know for sure is through lab-tested batches.
Limonene is a dominant terpene in cannabis strains with a pronounced sativa effect, appearing most often in sativa strains, but that doesn’t mean there aren’t indica strains with high limonene potential. Berry White exemplifies this. Jack Herer is a favourite with high levels of limonene and a palette of other terpenes like pinene and myrcene, which promote alertness and relaxation respectively. OG strains tend to have a lemony-pine aroma, which is limonene. It can be detected in Durban Poison, a high-energy sativa, even though not immediately apparent in its subtle sweet, earthy aroma, but you’ll feel its uplifting, stress-relieving effects. The presence of limonene in name and aroma is obvious with Super Lemon Haze, an uplifting sativa strain with a sweet lemon flavour.
Limonene can be vaporised at or around the terpene’s boiling point of 176°C (349°F).
A cyclic carbohydrate monoterpene, limonene is a main component of the essential oil of lemons, which is where its name comes from. It is present in citrus essential oils commonly used in Australia and widely used as a flavour and fragrance additive in cleaning and cosmetic products, food and pharmaceuticals. It is also a biodegradable, organic and environmentally friendly solvent for 3D printing and cleaning.
A major reason for limonene’s widespread use is its very low toxicity. While non-toxic to humans, an ‘allergic reaction’ (sensitisation and/or contact dermatitis) to limonene and linalool are more common than previously thought. Limonene may be related to α-pinene and some limonene products, oxidised by contact with air, provoke skin and mucous irritation. This leads to 3% of people exposed to high doses for a long period of time, such as workers in the paint industry, suffering from contact dermatitis. The second most widely distributed terpene in nature, limonene has a history in medicine and some studied therapeutic benefits include:
- Aiding digestion – treats indigestion and heartburn, prevents gastric distress by neutralising gastric acid and supporting normal peristalsis (digestive movement). Gastro-oesophageal reflux (GERD) is prevented.
- Anti-asthmatic – a 2010 study examined anti-inflammatory effects and found it to be a potential treatment for bronchial asthma due to its ability to inhibit cytokines.
- Anti-bacterial – naturally used by plants to kill pathogens and has anti-bacterial properties as discussed in a 2006 study.
- Anti-cholesterol – solvent of cholesterol; cholesterol-containing gallstones dissolve and “fat sludge” is cleaned from the Gallbladder. A 2011 study verified inhibition of the activity of an enzyme which plays a central role in the production of cholesterol.
- Anti-depression – relieves symptoms and elevates mood. A 2012 study examined it’s role and found it to be notable and a significant way to treat depression.
- Anti-fungal – natural remedy for athlete’s foot and yeast outbreaks.
- Anti-inflammatory – a potent anti-oxidant, studies from 2006 and 2010 explore such as an anti-inflammatory agent. A 2013 study went so far as to recommend using as a dietary supplement due to powerful anti-inflammatory effects on the intestines (controlling colitis).
- Anti-insomnia – improves sleep patterns and induces sedative effects.
- Anti-proliferative, chemo-preventive (prevents, rolls back and protects against cancer), inhibits cancer cell growth and helps fight the spread of various cancers (glioblastoma, prostate, pancreatic, breast and skin [melanoma]) – anti-carcinogenic activity in rat mammary carcinogenesis was evidenced in a 1993 study. In another 1993 study, evidence suggested chemo-preventive activity. It’s been known for over two decades it exhibits multiple anti-tumourigenic effects (1994). In 1995 collaborators re-evidenced it’s anti-carcinogenic ability. In a 1996 study, it was suggested it might be a chemo-preventive agent for colonic carcinogenesis. Shown in 1996 to inhibit carcinogen-induced lung tumourigenesis, a 1998 study suggested an association to anti-cancer activity in intercellular communication. Numerous studies and a clinical trial (1998) found it effective at beating advanced cancers and recommended further research. In 2002 effects were further investigated as a chemo-preventive agent against liver cancer and in a 2003 study it was demonstrated chemo-preventive. A 2007 study established chemo-preventive activity against many types of cancer including breast and colorectal. A selective anti-proliferative action on tumour lymphocytes was shown in 2008 along with inhibited metastatic progression of some melanoma cells. A 2010 study found a constituent increased the survival rate of glioblastoma patients and had virtually no long-term side effects. In 2010, citrus oil rich in limonene was verified to induce apoptosis (cell death) and act as an anti-angiogenic with a preventative effect on colon cancer. This effectiveness is being tested in clinical trials on breast cancer cells. A 2012 study found it to have strong enough inhibition of inflammation to actually be chemo-preventive. A 2013 study promoted the identification of pro-apoptotic, anti-inflammatory, anti-proliferative, anti-invasive and potential anti-angiogenic activities. A 2015 study demonstrated anti-cancer properties with effects on multiple cellular targets at varying potency.
- Antiseptic – has therapeutic effects in certain diseases and antiseptic properties, mainly against the bacteria responsible for acne.
- Anxiolytic (Anti-anxiety) – a 2012 study found it exhibited anxiolytic-like effects so potent and with such mild side-effects it was recommended as a new treatment for anxiety. Studies suggest it causes a rise of serotonin and dopamine neurotransmitters in the brain. Dispersal of it in the environment produces a decrease in depressive symptoms (trialled on hospital patients) in addition to a strong immuno-stimulation. It is quickly absorbed by inhalation or by the skin and it is metabolised quickly.
- Pre-Diabetes/Diabetes and weight loss – dietary use prevents and alleviates insulin resistance and works against development of the metabolic syndrome associated with non-alcoholic fatty liver disease (NAFLD). It acts as a mild appetite suppressant and prevents weight gain.
- Transdermal patches – improves absorption of other terpenes and chemicals by way of the skin, mucous membranes and digestive tract. Is being researched for use in dermal patches to improve transdermal absorption of other active substances as it aids in the biosynthesis of terpenes through the skin and mucous membranes (helps penetrate the skin).
Dietary Supplement that comes with a Warning
A person consuming one to two servings of citrus fruits per day is likely to get 15-40 milligrams (mg) of limonene; if the peels are consumed in some way this level may increase to 50-90 mg. The recommended dosage varies depending on the condition being treated, but most suggest taking 1,000 to 3,000 mg per day with meals. It is therefore deemed best to take limonene as a daily supplement to meet the daily dose required. Dietary supplements and essential oil blends of limonene are typically produced from the peels of oranges. Since using tinctures or undiluted essential oils can irritate the digestive passages, capsules are generally recommended for internal use. Typical brands sold at a health food store or online will contain between 250 to 1,000 mg per capsule.
People who have gastric ulcers or those who take medications which interact with grapefruit should consult their doctor before taking limonene. Higher doses than 3,000 mg or more (capsules) may cause the following:
- Feeling tired due to its calming and anti-anxiety properties
- Loose stools in some as it helps peristalsis (digestion)
- Could move stagnant bile rapidly into digestive tract, which may induce nausea (it clears sludge from the gallbladder)
Expanded from Myrcene, Linalool, and Bisabolol: What are the Benefits of These Cannabis Terpenes?, Limonene Safety FactSheet, Terpenes, Limonene, d-Limonene – Effective for Lowering Cholesterol Naturally and Much More, Antitumor Activity of Monoterpenes Found in Essential Oils, Infographic: What are Cannabis Terpenes and How Do They Affect You?, Terpenes, Chemistry and analysis of phytocannabinoids and other cannabis constituents, Evolution and Classification of Cannabis sativa (Marijuana, Hemp) in Relation to Human Utilization, Cannabinoids and Terpenes as Chemotaxonomic Markers in Cannabis, Plant terpenes: defense responses, phylogenetic analysis, regulation and clinical applications, d-limonene attenuates blood pressure and improves the lipid and antioxidant status in high fat diet and L-NAME treated rats, What is Limonene and Chemical profile, antifungal, antiaflatoxigenic and antioxidant activity of Citrus maxima Burm. and Citrus sinensis (L.) Osbeck essential oils and their cyclic monoterpene, DL-limonene