| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
[22] Methyldopa, oral (drug interaction with iron): Campbell N, Paddock V, and Sundaram R. Alteration of Methyldopa Absorption, Metabolism, and Blood Pressure Control Caused by Ferrous Sulphate and Ferrous Gluconate. ClinPharmacolTher, 1988, 43:381-6. https://www.ncbi.nlm.nih.gov/pubmed/3356082