Sheep sorrel historically has been used to treat inflammation, scurvy, cancer, and diarrhea. The major constituents include anthraquinones, tanins, oxalates, and various vitamins. The tannins have a drying effect on the nasal passages and reduce the mucous production and phlegm.This is why sorrel is used for reducing sudden and ongoing pain and swelling (inflammation) of the nasal passages in sinusitis.The blend of sorrel, gentian root, elder flower, verbena, and cowslip flower extracts is a classic herbal formula for treating sinusitis.Sheep sorrel is also used for treating respiratory and urinary bacterial infections, along with conventional medicines, and for increasing urine flow (as a diuretic). Caution: Check with your doctor if sorrel is safe to take if you have a medical condition and if you are taking other medicines.Consumption of large doses may result in diarrhea from the anthraquinones and renal and liver damage from the oxalate content. Do not use sorrel in the presence of kidney stones.There are no published trials evaluating the efficacy of sheep sorrel for any proposed claims.