WHAT ARE TERPENES?
Terpenes are aromatic organic compounds or essential oils that are found mainly in plants but also in some insects. Have you ever breathed in the soothing scent of lavender or caught a whiff of marijuana? It’s the terpenes in the plants that give them their distinctive smell and taste, just as flavonoids give plants their color. While terpenes are a component of most plants, they are almost always talked about in conjunction with marijuana as they are highly concentrated in the cannabis plant. There are over 20,000 terpenes altogether, over 100 of which are found in cannabis. In nature, terpenes are a defense system to stop plants getting eaten by herbivores or damaged by high temperatures. They also attract pollinators such as bees. For humans, different terpenes have different effects - including different health benefits. Each plant has a unique blend of terpenes. This is called its terpenes profile.
ARE TERPENES SAFE?
Terpenes are not psychoactive which means they don’t affect your mental processes or induce a high like the cannabinoid THC (tetrahydrocannabinol). Terpenes are recognized as safe by the FDA. If you think about it, all plants have terpenes and you eat them every day. So, when you breathe in the fresh scent of citrus as you enjoy your fruit in the morning, you're benefiting from terpenes. And people have used the scent of terpenes in essential oils to boost their emotional state for centuries.
WHY ARE TERPENES IMPORTANT?
Terpenes are important for a number of reasons. For people with health conditions and the medical marijuana industry, terpenes are important because as scientific knowledge about them increases, they can be used to create products that better target specific health disorders and diseases. Growers who produce marijuana for recreational use are also interested in terpenes because used carefully, terpenes can enhance a high, and influence the taste and smell of the product which means they can charge a premium price.
WHAT ARE THE HEALTH BENEFITS OF TERPENES?
This list of terpenes contains the most commonly used for health benefits. They are all found in cannabis, but as you will see, they are also common components of other plants too.
The most common terpene, myrcene can make up 50% of the terpene profile of a cannabis plant. Myrcene is also found in mangoes, hops, wild thyme, basil, and lemongrass.
Myrcene is often used to help people with insomnia. It is sometimes also used to reduce inflammation and relax muscles. 
Called a couch-lock terpene because of its sedative effect, myrcene can induce extreme tiredness and the feeling of being “stoned.”
Pinene is another common terpene, found in pine needles, orange peel, basil, parsley, sage, and conifer trees.
Alpha- and beta-pinene are powerful anti-inflammatories that may help promote airflow to your lungs (eg as a pre-workout drink), boost energy, mental alertness and memory.  Pinene is sometimes used to counterbalance short-term memory loss from the use of THC.
Limonene is found in citrus fruits such as lemons and oranges and in peppermint as well as cannabis. Because of its fresh scent, it is often used in cleaning products.
Limonene is mainly used as an antidepressant as it may help to elevate mood, relieve stress and boost energy.  Limonene is also considered to be an effective antifungal, antibacterial, weight loss aid, and is sometimes used to treat bronchial infections.
Limonene is often used in ointments and creams as it is thought to increase the absorption of other terpenes through the skin.
There has been a lot of discussion about the use of Limonene for cancer. Studies have suggested Limonene can stop cancer from spreading, promote the death of cancer cells, and even prevent cancer cells from forming in the first place. 
Alpha Bisabolol has a flowery scent and is found in plants such as chamomile. It is used for its antibacterial properties: to help heal wounds and fight inflammation. The cannabis strain, Oracle, is high in Alpha Bisabolol.
Borneol has a strong smell of camphor and is used as an antiseptic, pain-reliever, bronchodilator, and a sedative. Haze strains such as K13 are often high in borneol.
Delta-3-Carene has a strong smell of pine plus a spicy, floral aroma. It is found in bell peppers, cedar, and rosemary as well as pine needles.
Delta-3-Carene is often used as an anti-inflammatory and antihistamine. Because of this, it might help with some of the symptoms of Alzheimer’s disease and arthritis, and aid with bone repair.
Linalool is found in lavender, mint, cinnamon, coriander, and some mushrooms.
Linalool is often used to calm anxiety and aid sleep. Linalool is a powerful anti-inflammatory, and is used to promote neural function and control gross motor skills. It is also sometimes used by liver cancer patients, to boost the immune system, and reduce lung inflammation. Studies have suggested that it might help people with seizures and epilepsy. 
Beta-caryophyllene is the terpene found in leafy greens, basil, oregano, cinnamon leaves, black pepper, and cloves.
It is known as a gastro-protective, and also as an anti-inflammatory, antioxidant, and for pain relief. Beta-caryophyllene is often used to help people with anxiety and depression.
The results of an animal study carried out in China suggested that beta-caryophyllene could be useful in the management of Alzheimer’s disease as it might help reduce inflammation and activate CB2 (cannabinoid) receptors in the brain. 
Scientists also say that beta-caryophyllene could have anti-cancer properties, such as promoting the death of cancer cells, suppressing the growth of tumors, and stopping cancer from spreading. 
Camphene has a strong herbal taste and aroma. It is sometimes used as an anti-inflammatory and antibiotic and might help fight bacterial infections.
Terpineol smells like lilac and is often used in perfumes. Terpineol is found in the Jack strains of cannabis. It is used as an anti-inflammatory and antioxidant, to aid detox, and to fight fungal infections.
Eucalyptol is found in eucalyptus as well as many other plants. It has been used for centuries to reduce pain, and the results of modern medical studies appear to support this.
In one study, patients inhaled either eucalyptus oil or almond oil for 30 minutes for three days following a total knee replacement procedure. The eucalyptus oil group were shown to have reduced pain symptoms. 
Humulene is the terpene in hops, coriander, cloves, and basil. It is often used for its anti-inflammatory properties. Humulene is also used as a hunger-suppressant - this is in contrast to many other terpenes that lead to an increase in appetite rather than a decrease.
Terpinolene has smokey, woody fragrance and is found in plants such as sage and rosemary. Terpinolene is used as a sedative and is thought to have anti-inflammatory and analgesic properties.
HOW DO TERPENES WORK?
Trichomes grow on the flowers and leaves of female cannabis plants and look like tiny hairs. These trichomes contain cannabinoids such as CBD and THC, flavonoids that give the plant their color and terpenes. These are the compounds that are used for recreational and medical purposes.
The quality of the terpenes is affected by light, humidity, and temperature - so it’s essential that growing conditions are moderated closely. The plants also require careful handling during collection and processing to ensure the trichomes aren’t damaged.
Scientists used to believe that smells had positive health benefits because your sense of smell is associated with areas of the brain that influence your mood.
But they now believe that terpenes act directly on brain cells. They think terpenes work by binding to receptors and neurotransmitters and imitating natural compounds in your body to regulate emotions, weight, health etc.
THE ENTOURAGE EFFECT
Scientists say that terpenes in cannabis enhance the effect of cannabinoids such as THC and CBD leading to increased therapeutic benefits. This is called the entourage effect.
In groundbreaking research published in 2011 in the British Journal of Pharmacology, neurologist Ethan Russo suggested that cannabinoids and terpenes work together to increase the effectiveness of each other. 
Russo showed that terpenes help cannabinoids travel through the bloodstream and cross the blood-brain barrier.
Before that THC was thought to be the only chemical in cannabis with psychoactive capabilities. This research showed the potential of both CBD and terpenes to affect THC and the other chemicals in your body's endocannabinoid system (ECS). For example, myrcene combined with THC is a more effective sedative than THC alone.
Other contributing factors to the entourage effect include the proportion of cannabinoids such as THC and CBD, the way the cannabis plant is processed, how it is ingested, and the subspecies (indica or sativa).
Medical marijuana companies are creating blends of terpenes and cannabinoids to target certain health benefits.