Ginkgo nuts are used in "congee", and are often served at special occasions such as weddings and the Chinese New Year (as part of the vegetarian dish called Buddha's delight). In Chinese culture, they are believed to have health benefits; some also consider them to have aphrodisiac qualities. Japanese cooks add ginkgo seeds (called "ginnan") to dishes such as "chawanmushi", and cooked seeds are often eaten along with other dishes. When eaten in large quantities or over a long period, the gametophyte (meat) of the seed can cause poisoning by 4'-O-methylpyridoxine (MPN). MPN is heat-stable and not destroyed by cooking. Studies have demonstrated the convulsions caused by MPN can be prevented or treated successfully with pyridoxine (vitamin B6). Some people are sensitive to the chemicals in the sarcotesta, the outer fleshy coating. These people should handle the seeds with care when preparing the seeds for consumption, wearing disposable gloves. The symptoms are allergic contact dermatitis or blisters similar to that caused by contact with poison ivy. The first use as a medicine is recorded in the late 15th century in China; among western countries, its first registered medicinal use was in Germany in 1965. It has been used in traditional treatment of Alzheimer's disease. Despite use, controlled studies do not support the extract's efficacy for most of the indicated conditions. Although extracts of "Ginkgo biloba" leaf sold as dietary supplements may be marketed as being beneficial for cognitive function, there is no evidence for effects on memory or attention in healthy people. Gingko extract has also been studied for its role in preventing or slowing the onset of Alzheimer's disease. Studies have demonstrated mixed results. Systematic reviews have shown there is no evidence for effectiveness of ginkgo in treating high blood pressure, menopause-related cognitive decline, tinnitus, post-stroke recovery, peripheral arterial disease, macular degeneration, or altitude sickness. The use of "Ginkgo biloba" leaf extracts may have undesirable effects, especially for individuals with blood circulation disorders and those taking anticoagulants, such as warfarin or antiplatelet medication (e.g. aspirin), although studies have found ginkgo has little or no effect on the anticoagulant properties or pharmacodynamics of warfarin in healthy subjects. Additional side effects include increased risk of bleeding, gastrointestinal discomfort, nausea, vomiting, diarrhea, headaches, dizziness, heart palpitations, and restlessness.