1. Morphine: new aspects in the study of an ancient compound;Benyhe;Life Science,1994
2. A brief history of opiates, opioid peptides, and opioid receptors 90;Brownstein,1993
3. Antispasmodic effects of an alkaloid extracted from Phyllanthus sellowianus: a comparative study with papaverine;Calixto;Brazilian Journal of Medical and Biological Research,1984
4. Naturally occurring antinociceptive substances from plants;Calixto;Phytotherapy Research,2000
5. Biological activity of plant extracts: novel analgesic drugs;Calixto;Expert Opinion on Emerging Drugs,2001