Limonene is a terpene most commonly found in citrus plants. As the second most prevalent terpene on Earth, it can be found in the rinds of citrus fruits such as lemons, oranges, limes and more. It is the third most abundant terpene in cannabis and concentrates of up to 16% have been found in some strains. As a terpene, Limonene’s biological purpose is protective. Terpenes are aromatic compounds that ward off insects. However, when consumed along with cannabinoids by humans, terpenes may have beneficial medical effects. While limonene in normal quantities is not toxic to humans, it has been identifiable as a skin irritant in cosmetic products. Of course we're interested in what science says about the effects of limonene in cannabis when inhaled or eaten. The quick answer-- scientists don't know yet, but they have some ideas.
Benefits & Study Limitations
Citrus fruits have been used therapeutically for hundreds of years. Often, the source of citrus medicine has been orange and lemon peels. Modern science has begun to examine this through the exploration of limonene, a terpene with high concentrations in citrus peels. While limonene itself won't get you high, many consumers believe the terpene has properties that give it beneficial effects. Many of the studies we are about to dive into are promising, but it should be noted that real human trials need to be done before any scientific conclusions are made. Until there are real human trials regarding the consumption of limonene, these studies should be taken as a grain of salt and regarded as an interesting starting point for more research in the future. That said, terpenes are a fascinating subject and here are some of the reported effects and uses by researchers.
Our environments and the food we digest can cause our bodies to produce harmful cell waste called free radicals. Free radicals cause oxidative stress that can lead to conditions like cancer, heart disease, neurodegeneration, and immune deficiency. In a 2015 Food and Chemical Toxicology study, researchers found that limonene exhibits antioxidant effects in hamster cells. At varying doses, it was a non-toxic method of reducing oxidation-induced DNA damage.
A 2018 OncoTargets and Therapy study showed promising evidence that d-limonene may have a therapeutic effect on lung cancer in mice. In the study, d-limonene triggered apoptosis and autophagy, the body’s natural methods of killing and removing cancerous cells, in lung cancer tumors. However, the above results were achieved when the rodents were either injected with or ate foods rich in limonene. It should be noted that these test results might not completely relate to humans. After all, injecting a rodent with pure limonene isn’t exactly the same as a human smoking cannabis
Several studies have shown that limonene has a destructive effects on harmful bacteria, particularly food-borne pathogens like E. coli, Listeria, and food-spoiling yeast. Limonene also demonstrates antibacterial activity against staphylococcus aureus, or “staph” infection.
Increased interest in aromatherapy has led researchers to study the terpenes responsible for the supposed psychotherapeutic quality of fragrant terpenes. A 2013 Pharmacology, Biochemistry, and Behavior study on mice found that limonene demonstrated anxiety-reducing effects, calling limonene an “anti-anxiety agent.”
In his U.S. patent application for a method treating gastrointestinal disorders, inventor Joe Wilkins found that ingesting limonene capsules has a therapeutic effect on mild heartburn, GERD, and stomach acid indigestion. However, limonene has been found to exacerbate ulcer symptoms.
A 2019 Journal of Brazilian Society of Cardiology study found that d-limonene can reduce heart rate, blood pressure, and irregular heartbeat in rats. The results of the study led researchers to label d-limonene as a “promising substance” in the development of treatments for heart conditions like cardiac arrythmia. As with cannabis, more research is needed to understand the health mechanisms of limonene. Researchers must also further investigate the synergistic relationship between cannabinoids and terpenes like limonene.
How to Breed Strains for Limonene
If you know how you arrived on this planet, you have a general understanding of cannabis breeding. The dad gives the mom some pollen, and she makes a seed. It’s reproduction 101. If you want to breed a cannabis strain high in limonene, you’ll need to select parent plants that are also high in limonene. However, since the female traits tend to be passed down to the seeds more often than the male traits, it’s particularly important that you select a mother plant with high levels of limonene. The father should contain complementary traits. Contain the male and female plants in an enclosed environment to protect the female from being pollinated by any other plant than the one you’ve selected. One male plant can pollinate as many as 20 plants. To help along the pollination process, you can shake the male plant over the female plants or directly place the pollen from the male plant onto the females. The pollinated female will flower and produce seeds. For best results, you’ll want to grow these seeds and analyze the phenotype of each of the plants they produce. You can test these plants for their terpene content. As you strengthen your strain, you will select the plant with the most desirable phenotypes—in this case, elevated limonene content—to reproduce.
How to Tell if a Strain Has Limonene
Limonene has a crisp, sharp scent easy to recognize given its prevalence in beauty and cleaning supplies. So a long whiff of weed should help you detect its presence, right? Actually, probably not. A cannabis strain’s aroma is a symphony of scents created by its combined terpene profile. Additionally, limonene doesn’t always smell the same. It can smell like lemon, orange, or even grapefruit depending on its chemical expression. If you have a highly (read dog-like) sophisticated palate, you might be able to isolate the smell of limonene. Maybe. Strain names aren’t particularly illuminating, either. As you’re probably aware, cannabis strains are often named for anything but their actual chemical content. Though entertaining, these names aren’t particularly helpful in identifying terpenes. Even strains that have the name lemon in them can be misleading. For example, Lemon Meringue has limonene in it, but at lower concentrations than lots of other terpenes. The best way to truly identify the presence of limonene is through lab testing. Unfortunately, it’s not often that cannabis products list their terpene content. But it doesn’t hurt to look. Scan the label for a “Sum of Terpenes” section, and you may be pleasantly surprised.
Strains High in Limonene
Every cannabis plant has its own unique chemical profile. Cannabis flower from one Banana OG plant might contain .21% limonene, while another may contain only .11% of the terpene. With that in mind, the following strains generally have an elevated limonene content:
- White Widow: a hybrid commonly used to boost mood and appetite and reduce anxiety.
- Goji OG: a sativa-dominant strain that can increase focus and creativity but also trigger paranoia.
- Black Cherry Soda: a potent strain with a robust flavor profile and relaxing effect.
- Banana Kush: an indica-dominant strain known for producing a powerful body high.
- Banana OG: a uniquely flavored strain commonly used for sleep.
- Berry White: a hybrid known for promoting relaxation and focus.