4.Lizogub VG, Riley DS, Heger M. Efficacy of a Pelargonium sidoides preparation in patients with the common cold: a randomized, double blind, placebo-controlled clinical trial. Explore (NY). 2007;3:573-584. http://www.ncbi.nlm.nih.gov/pubmed/18005909
5.Bereznoy VV, Riley DS, Wassmer G, Heger M. Efficacy of extract of Pelargonium sidoides in children with acute non-group A beta-hemolytic streptococcus tonsil-lopharyngitis: a randomized, double-blind, placebo-controlled trial. Altern Ther Health Med. 2003 Sep-Oct;9(5):68-79. 7. http://www.ncbi.nlm.nih.gov/pubmed/14526713
6.Abraham K, Wöhrlin F, Lindtner O, Heinemeyer G, Lampen A. Toxicology and risk assessment of coumarin: focus on human data. Mol Nutr Food Res. 2010 Feb;54(2):228-39. http://www.ncbi.nlm.nih.gov/pubmed/20024932