Of the many active ingredients in marijuana, cannabinoids — the miracle molecules that deliver most of the plant’s medical efficacy — are not the whole picture. Some cannabis consumers may be aware of terpenes, the cannabinoid-like chemicals that give herb such a pungent aroma.
What most do not know is that terpenes also deliver therapeutic relief, just like their cousins the cannabinoids.
Terpenes are produced in special secretory cells within the trichomes of the plant, the nearly microscopic resinous stalks that cover the flowers and sometimes leaves. This is also where all cannabinoids, like THC and CBD, are created. About 20,000 terpenes exist in nature; more than 200 have been identified in cannabis (compared to 111 cannabinoids).
Like amino acids, terpenes are powerful building blocks within the plant’s physiology that aid in the production of vitamins, hormones, pigments, resins, and — yes, that most cherished part of the herb — cannabinoids. Cannabis plants release more terpenes when temperatures are higher.
Beyond odor, terpenes play several roles, including protecting the cannabis plant against predators like insects and animals. These special molecules constitute roughly 10 to 20 percent of the total pre-smoked resin in the trichome. It is estimated that 10 to 30 percent of smoke resin produced by marijuana comes from terpenes.
Limonene is a terpene that conveys a smell of citrus (orange, tangerine, lemon, lime, or grapefruit), juniper, rosemary, or peppermint. Lemons and other citrus fruits contain large quantities of limonene, especially in the rind. Thus, when one perceives an aroma of citrus in cannabis (or any other plant), it is literally the same chemical that produces this odor in fruits such as lemons, limes, and oranges.
While pleasant aromas are certainly desired on the part of recreational smokers, patients and the severely ill are more concerned with medicinal efficacy. Like myrcene, limonene has several medical benefits. It has been found to aid in digestion, to alleviate depression, and to contribute anti-bacterial and anti-fungal properties.
Limonene is also an anti-inflammatory, giving it efficacy for a number of conditions, and an anti-proliferative, meaning it is an effective anti-cancermedicine. The anti-cancer properties of limonene are what have generated the greatest media attention and are arguably the molecule’s most promising trait.
This therapeutic terpene is known to help fight anxiety and even treats acid reflux (heartburn). Limonene also can enhance one’s mood and has even been found to dissolve gallstones.
As with all areas of study of the medical qualities of cannabis, more research needs to be conducted to better understand the properties of terpenes like limonene. While human trials are in short supply, the fact that limonene does not appear on Schedule I of the Controlled Substances Act (unlike THC, CBN, and cannabis itself), it is easy to obtain and legal to use in studies.
A 2011 study conducted at the University of Arizona and published in the journal Oncology Reviews found that limonene has anti-cancer properties and is a modulator within the body’s immune system. The study concluded:
“…observations from cell culture, animal, and epidemiological studies support the presence of anti-cancer properties in citrus peel.”
A 2013 study conducted at the University of Arizona Cancer Center and published in the journal Cancer Prevention Research found that limonene was effective in preventing cancer cell proliferation and reducing tumor size. This human trial involved 43 women who had recently been diagnosed with breast cancer. A follow-on study in 2015 found similar results.
A study conducted in 2014 in France and published in the journal Anti-inflammatory and Anti-allergy Agents in Medicinal Chemistry reported that limonene has anti-inflammatory properties, making it valuable in the treatment of cancer (an inflammatory condition).
The study discovered that limonene possesses a “surprising” ability to prevent tumors from invading surrounding tissue by decreasing their ability to create new blood vessels. This powerful terpene was also found to play a role in the healing of skin and tissue regeneration.
Although those in prohibitionist states who must deal with the black market typically aren’t able to specify their choice of cannabis, several strains have shown to contain larger amounts of the limonene terpene. For those lucky enough to live in states with legal dispensaries and retail shops, the following strains can deliver a solid dose of limonene: