Mechanistic evidence of Andrographis paniculata (Burm. f.) Wall. ex Nees, Pelargonium sidoides DC., Echinacea Species and a combination of Hedera helix L., Primula veris L./Primula elatior L. and Thymus vulgaris L./Thymus zygis L. in the treatment of acute, uncomplicated respiratory tract infections: a systematic literature review and expert interviews - Veldman, LB M; Belt-Van Zoen, E; Baars, E W (Pharmaceuticals (Basel), 2023)