Limonene is a cyclic monoterpene that has a pronounced citrus odor and flavor, somewhat sweet yet tangy and bitter. Unsurprisingly, limonene is most commonly found in highest concentrations in the rinds of citrus fruit. Most of the research on the medicinal effects of limonene have focused on d-limonene, rather than other constituents of limonene like perillyl alcohol or a-limonene. A terpene with a wide range of uses, limonene is a commonly used terpene in perfumes, household cleaners, food, and medicines. Because of limonene’s widespread occurrence and application, its biological activity is well known. Limonene is highly absorbed by inhalation and quickly appears in the bloodstream Limonene is a chemical precursor to the terpenoid Carvone, and may be related to α-pinene.
Limonene has been said to modulate the affinity of THC for its own receptor, by sequestering THC, by perturbing annular lipids surrounding the receptor, or by increasing the fluidity of neuronal membranes
Limonene has numerous other medicinal benefits including promoting weight loss, aiding digestion, and preventing gastric distress. It has been shown to be an anti-fungal agent, and also shows promise as a treatment for anxiety and depression. Most interestingly, limonene has been shown both to stimulate the immune system and be an effective treatment for some cancer.
Limonene blocks the carcinogenesis induced by benz[α]anthracene (Crowell 1999), a component of the “tar” generated by the combustion of herbal cannabis. Thus, this terpenoid may reduce the harm caused by inhaling cannabis smoke. Limonene blocks carcinogenesis by multiple mechanisms. It detoxifies carcinogens by inducing Phase II carcinogen-metabolizing enzymes (Crowell 1999).