Learn about the aromatic compounds that give cannabis its distinct smell and make each strain unique.
By Martin A. Lee on March 01, 2014 (Updated on June 23, 2021)
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.
Terpenes and Cananbis’ Distinctive Effects
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.
Terpenes, or terpenoids, are the compounds in cannabis that give the plant its unique smell.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.
A Natural History of Terpenes
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 two hundred terpenes have been found in cannabis.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 genus Cannabis 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.
Common Cannabis Terpenes
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.
Related story Taming THC Beta-caryophyllene and the CB2 Receptor 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. The CB2 receptor regulates immune function and the peripheral 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. In 2008, the Swiss scientist Jürg Gertsch documented beta-caryophyllene’s binding affinity for the CB2 receptor and described it as “a dietary cannabinoid.” It is the only terpenoid known to directly activate a cannabinoid receptor (which is one of the reasons why green, leafy vegetables are very healthy for people to eat). The dual status of beta-caryophyllene as a terpenoid and a CB2 activator underscores the synergistic interplay between various components of the cannabis plant. There are over 400 chemical compounds in marijuana, including cannabinoids, terpenoids and flavonoids (which give fruit skin its color). Each has specific medicinal attributes, which combine to create a holistic “entourage effect,” so that the therapeutic impact of the whole plant is greater than the sum of its parts. What else can terpenes do? Certain terpenoids dilate capillaries in the lungs, enabling smoked or vaporized THC to enter the bloodstream more easily. Nerolidol, a sedative terpenoid, is a skin penetrant that increases permeability and potentially facilitates cannabinoid absorption when applied topically for pain or skin conditions. Terpenoids and cannabinoids both increase blood flow, enhance cortical activity and kill respiratory pathogens – including MSRA, the antibiotic-resistant bacteria that in recent years has claimed the lives of tens of thousands of Americans. Dr. Russo’s article reports that cannabinoid-terpenoid interactions “could produce synergy with respect to treatment of pain, inflammation, depression, anxiety, addiction, epilepsy, cancer, fungal, and bacterial infections.” Cannabinoid terpenoid interactions can amplify the beneficial effects of cannabis while reducing THC-induced anxiety.Marijuana’s bouquet of terpenes – that “riot of perfumes,” as the poet (and hashish eater) Arthur Rimbaud once said – plays another important role: Terpenes buffer THC’s tricky psychoactivity. Cannabinoid terpenoid interactions can amplify the beneficial effects of cannabis while reducing THC-induced anxiety. Some people can’t handle THC dominant marijuana, while others enjoy the relaxed intensity of the cannabis high. But few would willingly choose Marinol, the pure synthetic-THC pill, rather than organically grown backyard bud with its tangy, antioxidant-rich mixture of cannabinoids, terpenoids and flavonoids. Marinol, legally available as a Schedule III substance, comes on like gangbusters and can make even the most seasoned stoner feel a bit too loopy. For nearly everyone who has tried both, the experience of THC alone compares poorly to that of THC combined with terpenes and other components of the cannabis plant. Related story I’m Just Mad About Saffron Testing for Terpenes In the summer of 2011, the Werc Shop in Los Angeles emerged as the first lab to test cannabis strains for terpenes. Since it began providing this service to the medical marijuana community, the Werc Shop has analyzed more than 2,000 bud samples for terpene content. Its analysis has occasionally revealed strains with different names but identical terpene content. “A terpene analysis is like a fingerprint,” explains the Werc Shop’s president, Jeff Raber. “It can tell you if it’s the same strain under different names. We can see strains going by different names that have the same terpene profile. We now know those strains are identical.” Terpene testing has enabled the Werc Shop to identify when strains have been misnamed. “We’ve seen a dozen of samples of Trainwreck, for example, that have a consistent terpene profile,” Raber says. “And then we examine some bud purporting to be Trainwreck, but with a terpene content that differs markedly from what we know is Trainwreck. By testing for terpenes, we can often verify if the strain is what the grower or provider says it is.” It may be possible, via terpenoid and cannabinoid analysis, to investigate and verify the genetic lineage of various strains. Though a great deal of research would be required, one might even be able to construct something akin to a marijuana family tree. The Werc Shop has also tested numerous cannabis extracts for their terpene content. But Raber found that the oil-extraction process, if it involves heating the plant matter, typically destroys the terpenes, which evaporate at much lower temperatures than THC. Various extraction methods have their pros and cons. Using hexane or another toxic solvent to extract cannabis oil can leave poisonous residues behind. Critical CO2 extraction, while cleaner, requires expensive, sophisticated equipment and technical expertise. In either case, the extract maker may have to add the terpenes back into the oil concentrate in order to maximize the plant’s therapeutic potential. In the future, when the herb is legal nationwide, it should be possible to access strain-specific cannabis oils, as well as made-to-order marijuana extracts with a full array of terpenes artfully tailored to meet the needs and desires of individual users. Copyright, Project CBD. May not be reprinted without permission.