 This is a multicenter, double-blind, randomized, placebo-controlled, 6-arm study to investigate the optimal dose regimen, efficacy, and safety of cysteamine in the treatment of adult patients with CF who are experiencing an exacerbation of CF-associated lung disease. Patients will be screened for the study and eligible patients will be randomized to receive either cysteamine or placebo as add-on therapy to their standard of care treatment for CF-associated lung disease. 