Terpenes are compounds that give cannabis its unique smell and make each strain unique.
Terpenes have important therapeutic effects, as well.
By Martin A. Lee for Project CBD
March 01, 2014
The first thing you notice upon entering a well-stocked medical marijuana dispensary is the many varieties of cannabis on display – dozens of glass jars filled with glistening, manicured bud. Everyone has their favorites: OG Kush, Headband, Sour Diesel, Flo, Lemon Thai, Super Silver Haze… Some strains are energizing, some are sedating; some are better for pain, others for inspiration.
A couple hits of high-THC herb, by whatever name it’s called, will get you good and stoned. But it’s not the amount of delta-9-tetrahydrocannabinol that accounts for the particular properties of each strain. Nor are the minuscule quantities of cannabidiol (CBD) or the hundred or so “minor” cannabinoids a key factor in most strains. With few exceptions, the THC levels are lofty, while the other cannabinoids barely register their presence, according to labs that test samples for growers and dispensaries in states where medical marijuana is legal.
So if THC levels are generally high across the board and the other cannabinoids are present only at trace levels, what makes one strain different from another? And why does each marijuana strain impart a distinct psychoactive effect? There must be something else in the plant that influences the quality of the cannabis high.
David Watson, the master crafter of the foundational hybrid Skunk #1, was among the first to emphasize the importance of aromatic terpenes for their modifying impact on THC. Terpenes, or terpenoids, are the compounds in cannabis that give the plant its unique smell. THC and the other cannabinoids have no odor, so marijuana’s compelling fragrance depends on which terpenes predominate. It’s the combination of terpenoids and THC that endows each strain with a specific psychoactive flavor.
In 1989, Watson and his business partner, Robert Connell Clarke, formed HortaPharm, a legally chartered, Holland-based research company that specializes in botanical science and cannabis therapeutics. Based in Amsterdam, these two American expatriates broke new ground in horticultural pharmacology as they crossed and recrossed thousands of cannabis varietals, discarding most along the way while selecting a relatively small number for further development.
How did they decide which plants made the first cut? “We smelled them,” Watson explains.
He had long suspected that the terpenes present in cannabis resin enhance the potency of THC. Ten years after launching HortaPharm, Watson tested his hypothesis in an experiment that compared the subjective effects of 100 percent THC to lesser amounts in terpene-infused cannabis resin. The consensus among Watson and several associates: Terpene-infused resin with 50 percent THC was more potent by dry weight than an equivalent amount of pure THC.
Typically, terpenes are volatile molecules that evaporate easily and readily announce themselves to the nose. Therein lies the basis of aromatherapy, a popular alternative-healing modality. Like their odorless cannabinoid cousins, terpenes are oily compounds secreted in the marijuana plant’s glandular trichomes. Terpenes and THC share a biochemical precursor, geranyl pyrophosphate, which develops into the cannabinoids and terpenoids that saturate the plant’s flower tops.
But unlike THC and the other plant cannabinoids that exist nowhere else but in marijuana, terpenes are ubiquitous throughout the natural world. Produced by countless plant species, terpenes are prevalent in fruits, vegetables, herbs, spices, and other botanicals. Terpenes are also common ingredients in the human diet and have generally been recognized as safe to consume by the US Food and Drug Administration.
Scientists have identified and characterized the molecular structure of some 20,000 terpenes, which compose the largest category of plant chemicals. These can be further broken down into mono-terpenes, diterpenes and sesquiterpenes, depending on the number of repeating units of a five-carbon molecule called isoprene, the structural hallmark of all terpenoid compounds.
Around 200 terpenes have been found in cannabis, but only a few of these odiferous oily substances appear in amounts substantial enough to be noteworthy (or nose-worthy, as it were). Also, the terpenoid profile can vary considerably from strain to strain. “The range of flavors expressed by the genusCannabis is extraordinary – no other plant on the planet can equal the cacophony of smells and tastes available from cannabis,” says DJ Short, the breeder-artisan who conjured True Blueberry from several heritage landrace strains.
The terpenes in marijuana have given the plant an enduring evolutionary advantage. Some of these essential oils are pungent enough to repel insects and animal grazers; others prevent fungus. To combat plant disease and infestation, organic pot growers spray the terpene-rich essential oils of neem and rosemary onto their crops. And terpenes, it turns out, are healthy for people as well, according to a September 2011 report by Dr. Ethan Russo in the British Journal of Pharmacology that discussed the wide-ranging therapeutic attributes of terpenoids, including several aromatic compounds that figure prominently in cannabis strains.
- Alpha-pinene (essential pine oil), the most common terpene in the plant world and one often found in cannabis, is a bronchodilator potentially helpful for asthmatics. Pinene also promotes alertness and memory retention by inhibiting the metabolic breakdown of acetylcholinesterase, a neurotransmitter in the brain that stimulates these cognitive effects.
- Myrcene, another terpene present in numerous cannabis varietals, is a sedative, a muscle relaxant, a hypnotic, an analgesic (painkiller) and an anti-inflammatory compound. This musky terpene contributes mightily to the infamous “couch-lock” experience, Russo maintains.
- Limonene, a major terpene in citrus as well as in cannabis, has been used clinically to dissolve gallstones, improve mood and relieve heartburn and gastrointestinal reflux. Limonene, an anticonvulsant, has been shown to destroy breast-cancer cells in lab experiments, and its powerful antimicrobial action can kill pathogenic bacteria. (Lemon Kush, anyone?)
- Linalool, a terpenoid prominent in lavender as well as in some cannabis strains, is an anxiolytic compound that counters anxiety and mediates stress. In addition, linalool is a strong anticonvulsant, and it also amplifies serotonin-receptor transmission, conferring an antidepressant effect. Applied topically, linalool can heal acne and skin burns without scarring.
- Beta-caryophyllene is a sesquiterpene found in the essential oils of black pepper, oregano and other edible herbs, as well as in cannabis and many green, leafy vegetables. It is gastro-protective, good for treating certain ulcers, and shows great promise as a therapeutic compound for inflammatory conditions and autoimmune disorders because of its ability to bind directly to the peripheral cannabinoid receptor known as CB2.
THC also activates the CB2 receptor, which regulates immune function and the peripheral nervous system. But this is not the reason people feel stoned when they smoke marijuana; instead, what causes the high is THC binding to the CB1 receptor, which is concentrated in the brain and the central nervous system.
Stimulating the CB2 receptor doesn’t have a psychoactive effect because CB2 receptors are localized predominantly outside the brain and central nervous system. CB2 receptors are present in the gut, spleen, liver, heart, kidneys, bones, blood vessels, lymph cells, endocrine glands, and reproductive organs. Marijuana is such a versatile medicinal substance because it acts everywhere, not just in the brain.