Background & Aims: Helicobacter pylori (H. pylori) infection has been suggested as a cause of impaired drug absorption. This infection leads to alteration of the gastric acid secretion that may change the conformational characteristics of drugs and their intestinal absorption leading to uncertainties about the dose to administer and the therapeutic results. A systematic review was undertaken to clarify the implications of drug absorption during the administration of replacement therapies. Methods: Electronic databases such as MEDLINE/Pubmed, EMBASE and The Cochrane Library [which includes Cochrane Database of Systematic Review (CDSR), the Cochrane Central Register of Controlled Trials (CENTRAL), the Database of Abstract of Reviews of Effect (DARE)] were searched. Grey literature databases (e.g. the International clinical trials registry platform, Trials Register, Clinical Trials.gov, Controlled Trials and TrialsCentral), Theses database, Government publication and LILACS database were also searched. No language restriction was applied. Results: Infection and altered drug absorption were evaluated in patients under replacement therapies with iron, thyroxin and L-dopa. In all, seven studies included an improvement in drug absorption after eradication and an existing inverse correlation between the grade of gastric inflammation and indices of drug absorption were noticed. Conclusion: This systematic review confirmed the presence of an interaction between infection and drug absorption of orally administered replacement therapies. Gastric acid reduction and subsequent alteration of drug composition seem to lead this mechanism. Clinicians should be aware of this possible interaction when starting a replacement therapy in patients and when evaluating poor clinical response.