Magnesium stearate, an inactive ingredient added to most tablets and capsules so powders flow evenly without sticking to machinery, offers no demonstrated benefit for health or lifespan. Most concerns rest on laboratory cell studies, unsupported claims or animal feeding far above human amounts. For adults taking several supplements, it matters most with low-dose aspirin, a confirmed allergy to it, the tick-related red-meat allergy or medications that depend on steady absorption. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Alpha-gal IgE (only with suspected alpha-gal syndrome) | Below 0.1 kU/L | A positive result shifts use to vegetable-sourced or stearate-free products |
| TSH (only for levothyroxine users switching products) | 0.4–4.0 mIU/L | A shift after a formulation change signals altered absorption and prompts dose review |
| INR (only for warfarin users switching products) | No established target for a product switch; change from own pre-switch INR | A shift after a formulation change signals altered warfarin absorption and prompts dose review |
Cadence: TSH at 6–8 weeks after any levothyroxine product switch, then every 6–12 months as usual for that drug; INR within 1–2 weeks after any warfarin product switch; alpha-gal IgE once, not repeated unless symptoms recur. No routine laboratory testing for everyone else.