This was a summary of research (meta-study) on the bio-activity and effects of terpenes and terpenoids with cannabinoids. It was published in The Cannabinoid Journal online in December 2021. There are a number of points that are relevant to anyone considering cannabis products, since many include terpenes in significant amounts.
The authors noted that the terpenes & terpenoids found in cannabis & hemp flowers were different from those found in the lower fan leaves. The lower leaves were higher in bitter-tasting sesquiterpenoids (example: caryophyllene) to discourage grazers, and the upper flowers were higher in monoterpenes (examples: limonene and pinene) that discouraged insects.
There is also evidence that they interact with the human body in several ways.
"Terpenoids are pharmacologically versatile: they are lipophilic [they mix well with fats & oils, but not water], interact with cell membranes, neuronal and muscle ion channels, neurotransmitter receptors, G-protein coupled (odorant) receptors, second messenger systems and enzymes (Bowles, 2003; Buchbauer, 2010)."
They found reasearch that terpene concentrations of 0.05% or more are considered to be of "pharmacological interest". Most cannabis flower will have 10 or more different terpenes at or above that concentration level.
"Mice exposed to terpenoid odours inhaled from ambient air for 1 h demonstrated profound effects on activity levels, suggesting a direct pharmacological effect on the brain, even at extremely low serum concentrations"
The bioavailability of terpenes was demonstrated in several studies. The pulmonary absorbtion (from inhaling) of limonene was 70% and pinene was 60%.
This chart (from the article) shows a summary of their findings for eight common cannabis terpenes, including the cannabinoids known to possibly interact, and reinforce their effects:
There seems to be enough evidence to show that terpenes should be expected to contribute to, and possibly improve the effects of cannabinoids.