Limonene: Occurrence, Measurement, Research and Limits
Limonene is the citrus-scented terpene also found in cannabis. Learn how it is measured, what the human and lab research shows, and what safety questions remain.
Content last updated . This page has not been medically reviewed.
What limonene is
Limonene is a monoterpene, a ten-carbon aromatic molecule with the formula C10H16. PubChem lists its systematic name as 1-methyl-4-prop-1-en-2-ylcyclohexene. [1] It is one of the most common terpenes in nature and a major part of citrus oils such as orange, lemon, mandarin, lime and grapefruit. [2] It is also among the most common fragrance terpenes in everyday products. [3]Limonene exists in forms written (+) and (-). Most food-safety and human studies use d-limonene, which is the R-(+) form. [4] A study of one hemp variety reported (-)-limonene among its major terpenes. [5] Whether that difference matters for cannabis products was not examined in the sources read. This page is information only.
Evidence labels used here: preclinical (cells/animals only), promising but limited (a few small human studies), insufficient evidence, and marketing claim.
Where it occurs in cannabis
Cannabis makes limonene in its resin glands along with other terpenes. [5] In two small studies of cannabis chemistry, limonene was among the terpenes found in large amounts in two strains, [6] and among the major terpenes in ethanol extracts of most of six genotypes. [7] Another study found limonene higher in THC-dominant than in CBD-dominant varieties. [8]No typical percentage is given here. Reviewers note concern about lack of consistency in the terpene composition of cannabis "strains", [9] and cultivars in the same class can differ substantially in terpenes. [10] Only batch-specific laboratory data can show a particular product's limonene content. A name such as "lemon" or "citrus" on a menu describes aroma marketing, not a measurement.
How it is measured
Labs quantify limonene with gas chromatography, for example with flame ionization or mass spectrometry detection. [6] A headspace method reported a detection limit of 5 ppm for all analytes tested. [11] Because monoterpenes were lost when flower was turned into a CO2 extract in one comparison, a concentrate's limonene share can differ from its source flower. [12] See Terpene Testing: How Profiles Are Measured and Reported and How to Read a Cannabis Certificate of Analysis.What research shows
| Question | What was found | Evidence label |
|---|---|---|
| Anxiety caused by THC | In 20 healthy adults who use cannabis intermittently, vaporized d-limonene alone did not differ from placebo. Adding the highest tested d-limonene amount to THC reduced ratings of "anxious/nervous" and "paranoid" compared with THC alone, while other effects were unchanged and THC blood levels did not change. [13] | Promising but limited (one small study, one route) |
| Cancer prevention | In an open-label pilot of 43 women with early breast cancer, oral limonene reached breast tissue and lowered one tumor marker (cyclin D1), with minimal change in others. [14] The authors call for placebo-controlled trials. [14] | Insufficient evidence; biomarker change is not a clinical outcome |
| Mood, stress, sleep or energy from limonene in cannabis | Proper evidence not found. A PubMed search for human limonene trials returned trials of citrus oils and other uses, none testing cannabis limonene for these outcomes. | Insufficient evidence |
| Claims that a limonene-rich flower is "uplifting" | No source read supports this. A 140-flower study found no relation between terpene profiles and estimated effects. [15] | Marketing claim |
The anxiety study used vaporized THC at amounts that produced typical acute cannabis effects, and its authors say the results should be tested with oral products. [13] Do not read it as advice to combine anything. For THC's own risks see THC: Effects, Research and Risks.
Safety and limits
- Food and flavor use. A toxicology review concluded that d-limonene can be categorized as a low-toxicity additive. [4] A kidney effect seen in male rats depends on a rat-specific protein and was reported as not valid for humans. [4] The same review says toxicity of limonene breakdown products formed during storage is not known. [4]
- Skin. When limonene oxidizes it forms hydroperoxides that cause frequent positive patch-test reactions in people with dermatitis. [3] If a limonene-containing product irritates the skin, stop and ask a clinician.
- Heated inhalation. In a lab test, adding terpenes to THC raised gas-phase breakdown products from vaping and dabbing compared with THC alone. [16] That test did not isolate limonene. See Vape Liquids and Cartridges: Composition and Risks.
- Special groups. Pregnancy, children, older adults, and people with heart, liver or mental health conditions: Proper evidence not found for inhaled limonene from cannabis. See Cannabis Adverse Effects, Cannabis Use Disorder and Other Risks.
If a child or pet swallows a cannabis product, call US Poison Help at 1-800-222-1222, or 911 in an emergency.
Quality and labeling
Limonene is widely used as a flavor and fragrance, [4] so a label that lists limonene does not say whether it came from the plant or was added. See Added Terpenes vs Naturally Occurring Terpene Profiles and Terpenes in Cannabis.Frequently asked questions
Does limonene reduce anxiety?
One small double-blind study found vaporized d-limonene reduced THC-related "anxious" and "paranoid" ratings, but limonene alone matched placebo. [13] That is not enough to call it a treatment.
Is limonene from cannabis the same as limonene from oranges?
Both are called limonene and share the formula C10H16, [1] but they may not be the same form. Safety reviews describe d-limonene, the R-(+) form, [4] while a hemp study reported (-)-limonene. [5]
Is limonene safe?
As a food additive it was rated low in toxicity, [4] but oxidized limonene can cause skin reactions. [3] Safety of heated or concentrated limonene in cannabis products is not established by the sources read.
Does lemon scent on a label mean more limonene?
Not necessarily. Terpene content varies by batch, [6] and names and aromas are not laboratory measurements. [9]