Effects of Pycnogenol® in people with post-COVID-19 condition (PYCNOVID): study protocol for a single-center, placebo controlled, quadruple-blind, randomized trial. - Radtke, Thomas; Künzi, Lisa; Kopp, Julia; Rasi, Manuela; Braun, Julia; Zens, Kyra D.; Winter, Babette; Anagnostopoulos, Alexia; Puhan, Milo A.; Fehr, Jan S. (Trials, 2024)