Terpenes are scented molecules found in cannabis and many other plants, and responsible for flavour and aroma. Some of the most well-known terpenes found in cannabis are linalool, limonene, pinene, myrcene, and caryophyllene.
In addition to providing an aromatic experience, terpenes are believed to contribute to the effects of cannabis, both alone and in combination with cannabinoids. There is a lot of talk about the potential effects of terpenes on the body, but less talk about the mechanisms that explain these effects.
Are the effects of terpenes psychological, meaning they are due to expectations, beliefs, associations, and emotional learning associated with the scent? Or are they pharmacological, meaning they are due to interactions with receptors and hormones in the body? Evidence suggests that both mechanisms play a role in explaining how terpenes work.
The effects of terpenes: Pharmacological or psychological?
A 2009 review published in the International Journal of Neuroscience suggests that the effects of aromatic compounds can be explained either pharmacologically or psychologically.
The pharmacological hypothesis argues that aromatic compounds such as terpenes affect mood, physiology, and behaviour because they interact with the nervous and/or endocrine systems (hormones).
The psychological hypothesis argues that a person’s beliefs, expectations, emotional associations, and perceptions are the real reasons behind terpenes’ effects, not their direct interaction with systems in the body.
There is evidence for both hypotheses, which we will consider in turn.
There is plenty of research to support the idea that terpenes operate pharmacologically in the body and brain.
A 2001 review about the synergistic effects of terpenes in cannabis lists many potential mechanisms of action for these compounds, with its authors suggesting that terpenes may increase serotonin, norepinephrine, dopamine, and GABA activity. They argue that these effects may “support synergistic contributions of terpenoids on cannabis-mediated pain and mood effects.”
Although the natural world produces thousands of terpenes, very few have been studied for their specific mechanisms of action. Two exceptions are linalool, also found in lavender, and limonene, present in citrus fruits.
Linalool is known for its sedative, analgesic, and anti-inflammatory effects. Researchers believe linalool creates a sedative effect by decreasing sympathetic nerve activity and increasing parasympathetic nerve activity. (The sympathetic nervous system is responsible for the fight or flight response, and plays an integral role in waking behaviours. The parasympathetic nervous system opposes this activity, calming a person down and activating rest and digest.)
The mechanisms behind the pain-relieving effects of linalool are complex. A 2014 review suggests that linalool influences at least 10 different pain-related systems in the body. Linalool increases the activity of opioid receptors, as well as dopamine receptors. Linalool is also thought to inhibit the production of inflammatory cytokines, which explains its anti-inflammatory effects.
As for limonene, a 2013 study found that oral administration of lemon essential oil, which contains 70% limonene, had a significant antidepressant effect in a mouse model of depression. Researchers determined that the lemon oil increased the activity of serotonin, dopamine, and norepinephrine in different regions of the brain, which may explain its antidepressant effects.
Evidence of terpenes’ psychological effects
There is also evidence suggesting that terpene compounds may exert their effects – at least in part – through psychological mechanisms.
Liking or disliking an odour predicts a positive or negative shift in mood respectively. A 2003 study found that the odours a participant liked improved their mood, decreased anxiety, and decreased the unpleasantness of pain, and the odours they disliked worsened their mood and the way they felt about their pain. Similarly, psychological mechanisms can impact the way a person experiences the effects of cannabis. For example, a person who has had negative experiences with cannabis might find the scent to be anxiety-provoking, while someone who uses it at parties or in a social setting might associate it with fun.
Preconceptions matter, too. A 2004 study measured participants’ reactions to the suggested effects of different aromatic compounds. The results showed that the suggestion that an odour was relaxing was associated with decreased heart rate and skin conductance (a measure of physiological arousal), while the suggestion that an odour was stimulating increased these measures. This was true regardless of odour, and it was even true when no odour was used. The no odour condition produced relaxation or stimulation based on what was suggested. Lavender, which is considered to be a relaxing scent, was able to cause stimulation when this was suggested.
All this is to say that it is very likely that suggestion, emotional learning, beliefs, and expectations play at least some role in the way terpenes work. This doesn’t make the effects any less “real”, except that they might vary more between individuals than expected.
The bottom line
Both psychological and pharmacological mechanisms seem to contribute to the effects of terpenes.
There is good evidence suggesting that terpenes have direct physiological effects on the body, especially for linalool and limonene. This means that linalool-rich strains are likely to have a calming effect, and to provide pain relief, while limonene-rich strains are likely to be mood-elevating.
There is also good evidence to suggest that psychological phenomena such as expectations, beliefs, and associations play at least some role in the way terpenes affect the human body. This means that it’s important to listen to your intuitions about smell. If you dislike the scent of a particular strain, you might find you don’t like the experience either.
Future research will reveal much more about the way terpenes interact with our bodies and minds. It will be particularly important to study terpenes in the context of the many other compounds in whole-plant cannabis, such as cannabinoids, since many researchers believe these compounds all work together to produce effects they could not create alone.Researchers have only begun to scratch the surface when it comes to the way the terpenes in cannabis affect the body.