What Do Hot Peppers and Cannabis Have in Common?

A chilli pepper can discourage a seed-eating mammal, while a cannabis leaf rich in cannabinoids can be a poor meal for a caterpillar. The plants use very different chemicals, yet both offer examples of specialised metabolism: making compounds that influence interactions with the organisms around them. Research in wild chillies and Cannabis gives us unusually concrete evidence of what some of those compounds do.

Why do chillies make capsaicin?

Capsaicin is one of the capsaicinoids responsible for the heat of a chilli pepper. It is produced chiefly in the placental tissues inside the fruit, close to the seeds, rather than being distributed evenly through the flesh. The burning sensation matters to mammals, but birds are far less sensitive. This helps explain how a pepper can discourage some seed predators while still attracting birds that swallow and disperse its seeds (Tewksbury & Nabhan, 2001).

There is an equally interesting fungal story. Tewksbury et al. (2008) studied wild Capsicum chacoense in Bolivia, where pungent and non-pungent fruits occur in the same populations. In their field comparisons, seeds from pungent fruits had roughly half the fungal infection burden of seeds from non-pungent fruits. The researchers tested capsaicin and dihydrocapsaicin separately in artificial fruit media and found that both inhibited the growth of Fusarium, a fungus that damages pepper seeds. This was evidence for a protective role in that ecological system, not proof that every pungent cultivar resists every fungal disease.

What do cannabinoids do for Cannabis?

Cannabis produces a different group of compounds: cannabinoids, concentrated in glandular trichomes, particularly those covering female inflorescences and their bracts. These small secretory structures produce and store compounds in a resinous secretion alongside terpenes. Their development is covered in Trichomes: What Are They Actually For?.

One distinction matters when talking about THC. Living Cannabis plants mainly produce acidic cannabinoids, including THCA, CBDA and CBGA, in proportions that depend on the genotype. THCA can lose carbon dioxide and become THC, especially when heated. The compounds present in a living leaf or flower are therefore not necessarily the same as those discussed after heating or processing.

A particularly useful test of cannabinoid function comes from Stack et al. (2023). They compared Cannabis plants with different cannabinoid profiles and measured damage from leaf-chewing insects. Leaves containing more cannabinoids tended to suffer less chewing damage in field trials. In laboratory tests, cabbage looper caterpillars (Trichoplusia ni) ate less and grew less on cannabinoid-rich leaves. Adding cannabinoids directly to an artificial diet helped separate their effects from other differences between plants: increasing concentrations reduced larval growth and survival.

The main compounds tested in that work were associated with CBDA- and CBGA-producing plants; it was not a demonstration that higher THC in cannabis flowers prevents pest problems. Antimicrobial and UV-protective roles have also been proposed for cannabinoids, but evidence for those functions in living Cannabis plants is less direct. For a closer look at the chemistry and ecology, see Cannabinoids: Why Does the Plant Make Them?.

Similar purpose, different chemistry

Primary metabolism provides the materials and energy needed for growth: sugars from photosynthesis, amino acids for proteins and fatty acids for membranes, among many other functions. Specialised metabolism uses some of these resources to make compounds involved in defence, signalling and other ecological interactions. Phenolics, flavonoids, terpenes, alkaloids, capsaicinoids and cannabinoids are part of that broad chemical diversity. The older term secondary metabolites does not mean that these compounds are biologically unimportant.

The biochemical routes are quite different. Pepper capsaicin is made using components derived from phenylpropanoid metabolism and branched-chain fatty-acid metabolism. In Cannabis, olivetolic acid combines with geranyl pyrophosphate to form CBGA, which can then be converted into cannabinoid acids including THCA and CBDA (Antonio et al., 2018; Xie et al., 2023). The parallel is not that the plants share a recipe, but that they channel resources into specialised substances and concentrate them where they serve a purpose: around pepper seeds or in Cannabis trichomes.

Can stress increase the compounds growers want?

If defensive compounds can protect plants, can a little stress make cannabis produce more THC? Stress can alter specialised metabolism, but it can also reduce photosynthesis, growth and flower production. The result depends on the particular stress, its severity, duration, developmental stage and genotype. The protective role of a compound in one experiment does not establish a useful cultivation treatment.

There is also a difference between concentration and total production. If a plant produces fewer flowers, a higher cannabinoid percentage does not necessarily mean more cannabinoids per plant. The cannabis-specific findings, including cases where concentration and yield move in different directions, are discussed in Does Stress Increase THC or Terpenes?.

Breeding has changed both crops

People have selected chillies for pungency and Cannabis for cannabinoid profiles, concentrations and other traits. This selection has altered how strongly particular pathways are expressed and which compounds accumulate. It did not create those pathways from scratch. A particularly hot pepper or resin-rich cannabis flower reflects its genetics and development, not a general measure of health or resilience.

Where does plant signalling fit in?

Making a defensive compound is not the same as regulating a defence response. Salicylic acid, for example, is an internal plant signalling molecule involved in some defence pathways. Its role is explained in Plant Signalling: How Plants Know What to Do. PlantPotential provides composition and application information for Salic Signal, but findings about salicylic acid do not by themselves establish an effect of that formulation on cannabinoid production or plant resistance.

References

• Antonio, A. S., Wiedemann, L. S. M., & Veiga Junior, V. F. (2018). The genus Capsicum: a phytochemical review of bioactive secondary metabolites. RSC Advances, 8, 25767–25784. DOI: 10.1039/C8RA02067A.
• Stack, G. M., et al. (2023). Cannabinoids function in defense against chewing herbivores in Cannabis sativa L. Horticulture Research, 10, uhad207. DOI: 10.1093/hr/uhad207.
• Tewksbury, J. J., & Nabhan, G. P. (2001). Seed dispersal. Directed deterrence by capsaicin in chilies. Nature, 412, 403–404. DOI: 10.1038/35086653.
• Tewksbury, J. J., et al. (2008). Evolutionary ecology of pungency in wild chilies. Proceedings of the National Academy of Sciences, 105, 11808–11811. DOI: 10.1073/pnas.0802691105.
• Xie, Z., et al. (2023). Cannabis sativa: origin and history, glandular trichome development, and cannabinoid biosynthesis. Horticulture Research, 10, uhad150. DOI: 10.1093/hr/uhad150.