Caffeine vs Iron

for energy / fatigue

Stronger evidence: Iron

Stronger effect: Iron

Safety: Caffeine carries a minor interaction; Iron has none recorded.

For energy / fatigue, Iron has the stronger evidence grade.

grade B moderate certainty

reduces perceived fatigue; tolerance develops with regular use

40–200 mg

grade A high certainty

reliably reduces fatigue when iron deficiency / IDA is present; no benefit when iron-replete

18–65 mg/day, iron-deficient adults (esp. menstruating women)

sources: PMID:00000021 · PMID:10000007