As stated by Gaius, rosemary has the property of stimulating circulation. It also relieves headache pain, fights certain infections, stimulates digestion, and may inhibit some cancer cells. It is generally used for flavoring in cooking, as well as a useful ingredient in herbal medicine.
Edwin Muirden led Uther to believe that Gaius had almost killed Morgana by administering rosemary after misdiagnosing her with an inflammation of the brain. He claimed that she had suffered a cerebral haemorrhage, leading Gaius to admit that the rosemary may have increased the volume of the bleed. This led to Gaius being dismissed from his position as court physician.