Chaparral (Larrea tridentata) or known as the creosote bush is common in the Sonoran deserts of Mexico and the American southwest. The leaves and stems of L. tridentata contain high quantities of the phenolic compound: nordihydroguaiaretic acid (NDGA).

In a recent study printed in the 2009 addition of; European Journal of Pharmacology conducted by: U.C. San Francisco department of medicine concluded:

"NDGA blocks the DHT-induced growth of LAPC-4 prostate cancer cells by several mechanisms including rapid inhibition of the IGF-1R kinase, and a dose-dependent inhibition of androgen stimulation of IGF-1R expression."

In another study conducted by: Division of Diabetes and Endocrine Research at San Francisco/Mt. Zion Medical Center and published in; Breast Cancer Research and Treatment stated:

"We can now attribute certain of these anti-cancer properties in breast cancer cells to the ability of NDGA to directly inhibit the function of two receptor tyrosine kinases (RTKs), the insulin-like growth factor receptor (IGF-1R) and the c-erbB2/HER2/neu (HER2/neu) receptor."

Combined research from Department of Chemistry, National Tsing Hua University, Taiwan; Department of Chemistry, National Central University, Taiwan; and Department of Biology, Johns Hopkins University, Baltimore, concluded:

"A series of new nordihydroguaiaretic acid derivatives were prepared and screened, which exhibited inhibitory activity against HIV ... These new compounds exerted appealing activity against HIV Tat-regulated transactivation in human epithelial cells."

An earlier study was published conducted by Department of Biochemistry and Molecular Biology; The Ben May Institute for Cancer Research; and The Tang Center for Herbal Medicine Research, University of Chicago which demonstrated a direct inhibition of 5α-reductase type I, which can prevent the conversion of testosterone to dihydrotestosterone (DHT). It has been well documented that DHT is the primary cause of androgenic alopecia among other androgen-dependent disorders such as prostate cancer. The study states (paraphrased):

"Certain natural products contain components that are inhibitors of 5α-reductase. Some compounds were more effective inhibitors of the type 1 isozyme, including nordihydroguaiaretic acid NDGA among others"

Chaparral side effects:

Several cases have been reported which include; allergic reactions including rashes, itching, inflammation of the mouth and fever. In some reported cased ingestion of chaparral has lead to hepatoxicity and kidney failure. It may also increase blood sugar levels an act as a blood thinner.

Chaparral drugs interactions:

Chaparral may also cause an under-expression of the liver enzyme cytochrome P450 causing the levels of other drugs or supplements to rise leading to drug side effects.