

R-limonene, orange peel oil, citrus peel oil, citrene
Derived from the peels of citrus fruits, D-limonene is used by patients to prevent and treat cancer and has been promoted as a treatment for gastroesophageal reflux. Following oral administration, D-limonene is rapidly metabolized to limonene-1,2-diol, perillic acid, dihydroperillic acid, and uroterpenol (1) (2) (3).
In vitro and animal studies suggest that D-limonene has anti-inflammatory (13) and anticancer effects (14). It was also shown to enhance the activity of docetaxel against prostate cancer cells (15).
An epidemiological study reported an inverse relationship between citrus peel consumption and squamous cell carcinoma (4), but an early clinical trial in breast cancer patients failed to support the observations (5) (6).
Further research is necessary to determine if D-limonene has a role in the prevention or treatment of cancer.
Although the exact mechanism of action is unknown, D-Limonene and its metabolites, perillic acid, dihydroperillic acid, uroterpenol, and limonene1,2-diol, may inhibit tumor growth via inhibition of p21-dependent signaling and apoptosis resulting from induction of the transforming growth factor beta-signaling pathway (9) (10). D-Limonene metabolites also cause G1 cell cycle arrest, inhibit posttranslational modification of signal transduction proteins, and cause differential expression of cell cycle- and apoptosis-related genes (6). Animal studies show activity of D-limonene against pancreatic, stomach, colon, skin, and liver cancers (5). Data also indicate that D-limonene slows the promotion/progression stage of carcinogen-induced tumors in rats (11) (12).
Following oral administration, D-limonene is absorbed rapidly and metabolized to perillic acid (PA), dihydroperillic acid (DPA), limonene1,2-diol, and uroterpenol. D-Limonene metabolites distribute throughout the body to all sites, including adipose tissue, and are eliminated as glucuronide metabolites in the urine (1) (2) (3).
None known
Vigushin DM, et al. Phase I and pharmacokinetic study of d-limonene in patients with advanced cancer. Cancer Research Campaign Phase I/II Clinical Trials Committee. Cancer Chemother Pharmacol 1998;42:111-7.
A phase I pharmacokinetic study was conducted with doses ranging from 500-12000 mg/m2/day. A single tumor response was documented in a breast cancer patient at the 8000 mg/m2/day dose level. The investigators conducted a small phase II study with 10 additional breast cancer patients but no additional tumor response was noted. Side effects include nausea, vomiting, and diarrhea. Additional studies are necessary to establish efficacy of D-limonene.
Bottom Line: D-limonene has not been shown to be an effective cancer treatment in humans.
D-limonene is made from the peels of citrus fruits. Scientists are not exactly sure how it works, but it showed some anticancer activity in laboratory studies. These studies suggest that D-limonene alters the signaling pathways within cancer cells in a way that stops cancer cells from multiplying and causes their death (this is called “apoptosis”). In animals, D-limonene slowed the growth of pancreatic, stomach, colon, skin, and liver cancers. It also slowed formation of tumors and their progression in animals exposed to cancer-causing substances. However, these anticancer effects have not been shown in humans.
Cancer treatment:
Researchers conducted a two-part study to assess the effectiveness of D-limonene in treating solid tumors that had not responded to other therapies. In the first part, 32 patients with solid tumors received a range of doses of intravenous D-limonene in order to identify how high the doses could go without causing toxic side effects. Because one breast cancer patient showed a partial response (shrinkage of her tumor), ten additional breast cancer patients were added to the study and were given 8 g/m2/day of D-limonene. However, none of these patients showed any tumor shrinkage. This small study does not support d-limonene as a cancer treatment.