The results of a study suggest carnosic acid, found in rosemary, may shield the brain from free radicals, lowering the risk of strokes and neurodegenerative diseases like Alzheimer's disease and Amyotrophic lateral sclerosis, and is anti-inflammatory. Carnosol is also a promising cancer chemoprevention and anti-cancer agent. A study found that rosemary "produced a significant enhancement of performance for overall quality of memory and secondary memory factors, but also produced an impairment of speed of memory compared to controls."

Rosemary contains a number of potentially biologically active compounds, including antioxidants carnosic acid and rosmarinic acid. Other bioactive compounds include camphor (up to 20% in dry rosemary leaves), caffeic acid, ursolic acid, betulinic acid, rosmaridiphenol and rosmanol. Rosemary antioxidants levels are closely related to soil moisture content.^[ Rosemary may have some anticarcinogenic properties. A study where a powdered form of rosemary was given to rats in a measured amount for two weeks showed a reduction in the binding of a certain carcinogen by 76%, and greatly reduced the formation of mammary tumors.