Terpenes: Why Does the Plant Make Them?

Cannabis can produce aromas reminiscent of lemon, pine, pepper, flowers or fuel. Terpenes contribute to this variety, but their biological roles extend beyond the smell and flavour we notice. Across plants, these compounds participate in defence, interactions with insects, volatile signalling and responses to environmental conditions.

To understand why Cannabis produces them, it is useful to separate the chemistry demonstrated in Cannabis from ecological functions established in other species. The presence of a compound does not, by itself, establish its role in a living plant.

What is a terpene?

Terpenes are a large family of carbon-based compounds produced throughout the plant kingdom. Cannabis produces substantial amounts in the glandular trichomes covering female flowers. Researchers have identified more than 100 terpenes in Cannabis, although a smaller group normally dominates the terpene profile associated with aroma.

Common examples include myrcene, limonene, α-pinene, β-pinene, linalool, β-caryophyllene, humulene and ocimene. Cannabis terpene synthase genes involved in producing many of these compounds are expressed particularly strongly in glandular trichomes.

Monoterpenes and sesquiterpenes

Two groups are particularly important in Cannabis. Monoterpenes contain ten carbon atoms and include myrcene, limonene and pinene. Sesquiterpenes contain fifteen carbon atoms and include β-caryophyllene and humulene.

Many monoterpenes are highly volatile, meaning they readily enter the air and contribute to aroma. Sesquiterpenes are generally less volatile and can remain associated with plant tissues for longer. The balance between these groups changes during development, with terpene production influenced by genotype, developmental stage and trichome maturation.

Where are Cannabis terpenes made?

Much of the terpene-rich resin associated with female Cannabis flowers is produced in glandular trichomes. Their secretory cells contain specialised metabolic machinery, including terpene synthases that convert common precursor molecules into different terpene structures. The products accumulate alongside cannabinoids in the extracellular storage cavity of the trichome head.

This connects aroma with resin production and the glandular structures visible on flowers. Trichomes nevertheless have broader biological roles than storage alone, and their appearance does not directly measure the amount of each compound present.

Terpenes can be chemical defence

Across plant species, terpenes can repel herbivores, reduce feeding, interfere with insect development or contribute to toxic or deterrent mixtures. Plants attacked by herbivores may also change the blend of volatile compounds they release.

These blends are known as herbivore-induced plant volatiles, or HIPVs, and terpenoids form an important part of many such mixtures. Their defensive contribution depends on the compounds, concentrations, plant species and organisms involved rather than on aroma strength alone.

Volatiles can contribute to indirect defence

Some volatiles released by an attacked plant attract organisms that attack the herbivore. For example, volatile blends can help parasitoids and predatory insects locate plants containing suitable hosts or prey. This is described as indirect defence.

β-Caryophyllene, β-ocimene and other volatile terpenoids participate in these multitrophic interactions in different plant systems. The response is an ecological interaction between organisms, not evidence that a plant consciously calls for assistance or that the same blend will attract beneficial insects in every crop.

Volatiles can prime neighbouring tissues

Neighbouring leaves, and sometimes neighbouring plants, can respond to volatile organic compounds released during herbivore attack. Exposure can prime defence responses, preparing a tissue to respond faster or more strongly if an attack follows without necessarily activating its full defence immediately.

Research across plant species supports these volatile-mediated interactions, although the sensing mechanisms for many individual compounds remain under investigation. This connects terpene ecology with the broader distinction between defence activation and signalling and preparation.

Does Cannabis use its terpenes this way?

The ecological functions of terpenes are well documented across the plant kingdom, and Cannabis produces terpene-rich resin in glandular trichomes. Direct Cannabis experiments have also shown that cannabinoids can reduce the feeding and performance of chewing herbivores.

That cannabinoid evidence does not establish the contribution of individual Cannabis terpenes, nor does evidence of indirect defence or volatile priming in another species demonstrate the same interaction in Cannabis. These are plausible connections that require their own crop-specific experiments.

What about microbes?

Many terpenes show antibacterial or antifungal activity under laboratory conditions, making antimicrobial defence a plausible function of terpene-rich glandular secretions. Inhibiting a fungus in a laboratory assay does not automatically demonstrate protection on a living Cannabis plant or identify the compound's primary ecological role.

The same molecule may influence herbivores, microbes, neighbouring plants, predators or the plant's own physiology. These possible functions should be assessed separately rather than treating a laboratory antimicrobial result as evidence of general crop protection.

Why are terpenes volatile?

Volatility allows molecules to enter the air and influence organisms at a distance, which helps explain their role in ecological signalling. It also makes retained aroma sensitive to post-harvest conditions.

Terpenes can be lost during drying, particularly with high temperatures, as well as through handling and prolonged storage. Airflow can influence removal of emitted volatiles, although ventilation is also needed to manage moisture. These relationships are reasons to control post-harvest conditions, not to eliminate airflow.

Aroma in the drying room indicates that volatile compounds are entering the air, but its intensity does not quantify the amount lost from the flowers.

Are terpenes “secondary metabolites”?

Cannabinoids, terpenes, capsaicinoids, flavonoids and related compounds are often discussed as secondary metabolites. The term specialised metabolites is also used, particularly when considering compounds involved in ecological interactions rather than treating them as incidental products of growth.

A pepper's investment in capsaicinoids and Cannabis production of cannabinoids and terpenes involve different chemistry, but both illustrate how specialised compounds can contribute to interactions with the environment, survival and reproduction. This does not mean every member of the broad terpene family has the same specialised function.

Does stress increase terpenes?

Stress can alter specialised metabolism, but it does not reliably increase every terpene or improve overall crop performance. A 2025 Cannabis study examining water deficit and abscisic acid during early flower development and after recovery illustrates the importance of timing.

During early flowering, water deficit increased sesquiterpene concentrations while cannabinoids decreased. After recovery, monoterpene concentrations were higher than in control plants and cannabinoid responses had changed again. The response therefore depended on when the treatment occurred and when the plants were measured.

These findings do not establish a universal stress treatment for improving Cannabis. The article Does Stress Increase THC or Terpenes? examines the production trade-offs. For the broader physiology, see Do plants get stressed out?

Concentration is not total production

A higher percentage does not necessarily mean a plant produced more of a compound. In a hypothetical example, flower biomass might fall by 30% while one terpene increases from 1.0% to 1.2%. The concentration has increased, but the total amount produced can still be lower.

Stress treatments therefore need to be evaluated using both concentration per gram and total production per plant. The same distinction applies to cannabinoids; a concentration result alone does not establish a production benefit.

Do terpenes define the effect of Cannabis?

Terpenes contribute strongly to aroma. Whether they substantially alter the pharmacological effects of cannabinoids through a broad “entourage effect” is a separate question and should not be assumed because cultivars smell different.

The ecological functions of these molecules are also independent of their possible effects in humans. Evidence about plant defence or volatile signalling cannot establish a particular human response to a Cannabis aroma profile.

Genetics matters enormously

Cannabis cultivars grown under the same conditions can produce different terpene profiles. Different terpene synthase genes, their variants and their expression levels contribute to these differences, while the environment modifies the expression of that genetic potential.

The final aroma consequently reflects genotype, development, environment and post-harvest handling rather than a response to a single nutrient or cultivation treatment.

More smell does not necessarily mean more terpenes

Odour thresholds differ between compounds, and human perception is particularly sensitive to some molecules. Small changes in a volatile profile can therefore produce a substantial perceived difference.

Conversely, a high total terpene concentration does not guarantee a proportionately stronger perceived aroma. Smell reflects the composition of a mixture and the observer's sensory response, not a direct measurement of total terpenes.

The bigger picture

Terpenes are part of the chemical interactions between plants and their environment. Across species, they can participate in defence, volatile signalling and responses to changing conditions. In Cannabis, their production is closely connected to glandular trichomes and varies with genetics, development and environmental conditions.

Understanding these compounds means keeping their demonstrated production biology separate from ecological functions that remain to be tested directly in Cannabis. That distinction makes aroma informative without treating it as a measure of crop health, chemical concentration or therapeutic effect.

References

Booth, J.K. et al. (2017). Terpene Synthases from Cannabis sativa. PLOS ONE, 12, e0173911.

Tanney, C.A.S. et al. (2021). Cannabis Glandular Trichomes: A Cellular Metabolite Factory. Frontiers in Plant Science, 12, 721986.

Hancock, J., Livingston, S.J. & Samuels, L. (2024). Building a biofactory: Constructing glandular trichomes in Cannabis sativa. Current Opinion in Plant Biology, 80, 102549.

Jin, W. et al. (2025). A Comprehensive Review of Plant Volatile Terpenoids, Elucidating Interactions with Surroundings, Systematic Synthesis, Regulation, and Targeted Engineering Production. Biology, 14, 466.

Arimura, G. & Uemura, T. (2025). Cracking the plant VOC sensing code and its practical applications. Trends in Plant Science, 30, 105–115.

Regulation of secondary metabolism in Cannabis sativa L. by abscisic acid and water deficit during early flower development and after recovery. Plant Stress, 18, 101074 (2025).