1. von Reis Altschul S. Exploring the herbarium. Sci Am 1977; 236: 96-114.
2. Phillipson JD. Global trend and market size of herbal medicine in primary health care. In: Chan KL, Hussin AH, Sadikun A, Yuen KH, Asmawi MZ, Ismail Z, editors. Trends in Traditional Medicine Research. Penang: Universiti Sains Malaysia; 1995.
3. Johnstone BA. One third of nation’s adults use herbal remedies. Herbalgram 1997;40:49.
4. Center for Disease Control, Atlanta, Georgia. Morbidity and Mortality. Weekly Report 1978; 27:51.
5. Dobb GJ, Edis RH. Coma and neuropathy after ingestion of herbal laxative containing podophyllin. Med J Aust 1984; 140:495-496.