Short Answer
Limonene is a monoterpene with the formula C10H16. It makes up most of the oil in orange, lemon, and grapefruit peel. In humans, oral limonene at 1 to 2 grams per day reduced heartburn symptoms in one small trial. Inhaled limonene changes mood ratings: several studies report less anxiety and more alertness. Evidence for the mood claims is weak. Most human studies are small, short, and use different doses. Limonene is also one of the most common terpenes in cannabis flower.
What Limonene Does in the Body
Swallowed limonene is absorbed in the gut and broken down in the liver. Enzymes CYP2C9, CYP2C19, and CYP3A4 convert it into perillic acid and related metabolites. Those metabolites leave the body in urine. Inhaled limonene reaches the blood through the lungs. Limonene also triggers smell receptors. Some of the calm and alertness people report after smelling citrus comes from odor perception, not from a drug effect.
Limonene Effects Review: What to Expect at a Cannabis Store
Animal studies show anti-inflammatory and antioxidant activity. Doses in those studies run far above what a person gets from a cannabis product.
Reported Effects
- Mood: small trials report lower anxiety scores after limonene inhalation. Sample sizes are often under 50 people.
- Alertness: some participants report feeling more awake. Results differ between studies.
- Digestion: 1 to 2 grams per day by mouth reduced reflux symptoms in a trial of 19 patients.
- Skin: oxidized limonene causes contact allergy. Patch test rates for limonene allergy run from 1% to 3% in dermatology clinics.
Limonene in Cannabis
Limonene appears in cannabis flower at about 0.05% to 0.5% of dry weight in tested samples. Total terpene content in flower runs about 0.1% to 3%. One gram of flower at 0.2% limonene holds about 2 milligrams of the compound. That is far below the 1,000 milligram dose used in clinical work. Store staff who say limonene in flower drives a specific high are going past the data.
Limonene in Cannabis: What to Expect at the Dispensary
Dose, Safety, and Rules
d-Limonene holds GRAS status from the FDA as a food flavoring. Rat oral LD50 values sit near 4.4 grams per kilogram. Side effects at high oral doses include nausea, diarrhea, and stomach cramping. Limonene induces some liver enzymes, so it can change blood levels of drugs that use those pathways. Cannabis products carry their own warnings. Limonene content on a label is not a medical claim.