Sage leaves. Sage leaves contain an oil that is being investigated for its medicinal effects. Sage has been used by herbalists for centuries to improve memory, and a medical trial in 2003 showed improved short-term memory recall in those given sage oil tablets. It is thought that sage oil tablets could slow the onset of Alzheimer's disease. Sage species being investigated include Salvia lavandulaefolia and Salvia officinalis. These leaves are part of research being carried out at laboratories at the Universities of Newcastle and Northumbria, UK, as part of work by the Medicinal Plant Research Centre.