What is terpene limonene and what are its properties?

Terpenes are fragrant oils that are secreted along with cannabinoids like THC and CBD, and these terpenes not only determine the smell of a cannabis varieties, but can also alter its effects. Terpene limonene is an aromatic cannabis terpene produced in the resin glands of the flower. In isolation, it is commonly associated with fruity citrus aromas and is found in many everyday items such as fruit peels, cosmetics and cleaning products. While it is often assumed that limonene is abundant in cannabis varieties that smell like lemon, this is not always the case. If you are looking for cannabis varieties with high limonene content, you need to find lab-tested products to be sure that the variety you are buying actually has limonene in it. While THC typically makes up 10-30% of the dry weight of a flower, limonene is present in trace amounts, usually less than 2%.

Possible effects and benefits of limonene

Despite the potential therapeutic benefits of terpene limonene, little is known about how it works in the brain and body and what doses are required to achieve these benefits. Many of the limonene studies to date have used high doses – much higher than the amounts found in cannabis. More research is needed on cannabis, but the studies on limonene so far have shown that it has potential in the following areas of use:

• Elevated mood
• Stress relief
• Antifungal properties
• Antibacterial properties
• May help relieve heartburn and gastric reflux
• Improves absorption of other terpenes and chemicals through the skin, mucous membranes and digestive tract

There are also promising indications of terpen limonene’s tumour-inhibiting effect. In laboratory rodents, limonene inhibited the growth of skin and breast tumours. Following these studies, a phase I clinical trial was conducted in humans, which found that limonene was able to reduce the growth of breast cancer tumours to some extent for almost a year. Later studies found that daily intake of limonene for a period of 2 to 6 weeks silenced a protein that promotes the growth of breast cancer tumours, suggesting that daily intake of limonene may inhibit the growth and spread of breast tumours.

Other reports have shown that limonene has a beneficial effect in laboratory models of lung and brain cancer by causing the death of tumour cells. However, as with limonene’s effect on breast cancer, high doses beyond those found in cannabis alone are likely to be required. It is not known, however, whether the presence of certain cannabinoids enhances limonene’s anti-cancer effects. At present, there is not nearly enough evidence to conclude that cannabis products with a high limonene content are effective as a cancer treatment in humans.

Future research on limonene

It is still unclear how terpene limonene achieves its therapeutic effects. Inhaling limonene vapour increases serotonin and dopamine levels in key regions of the brain associated with anxiety, depression and obsessive-compulsive disorder. Does limonene merely stimulate the brain’s olfactory system, or does it directly affect the brain cells themselves? We don’t know yet. Unlike some other terpenes that have well-defined targets in the brain, such as linalool and B-caryophyllene, limonene’s targets are still unclear. As scientists better understand limonene’s targets in the brain and body, they can help users find cannabis varieties or products where limonene’s therapeutic benefits are optimised by a specific cannabinoid and terpene profile.

High-limonene cannabis varieties

Some cannabis varieties have higher limonene content than others, but these levels can vary greatly from crop to crop depending on genetics, growing techniques and curing processes. The only way to find out if your variety has a high limonene content is through lab-tested batches.

Cannabis varieties with a high limonene content