Magnesium Glycinate vs L-Threonate vs Citrate: A Form-by-Indication Guide

All three forms are safe at standard supplement doses. The key safety points to be aware of: **Upper limit:** FDA tolerable upper intake for supplemental magnesium is 350mg elemental Mg/day for adults. This limit refers to supplements, not dietary magnesium. Exceeding this increases diarrhea risk and, in individuals with reduced kidney function, hypermagnesemia risk. **Kidney disease:** All forms require physician supervision in CKD (eGFR <30 mL/min). Kidneys regulate magnesium excretion; impaired kidneys cannot compensate for excess intake. **Drug interactions (all forms):** Magnesium binds tetracycline antibiotics and bisphosphonates, reducing their absorption. Separate magnesium supplementation from these medications by at least 2 hours. Magnesium may enhance the effect of muscle relaxants and blood pressure medications. **L-Threonate specific:** The very low elemental Mg content (144–200mg/day from 2g salt) means it does not contribute substantially to total supplemental Mg burden. This is actually a relative safety advantage for stacking. **Citrate specific:** The laxative effect at higher doses is dose-dependent and predictable. Staying at or below 200mg elemental Mg from citrate typically avoids significant GI effects in most adults. **Medication and diagnosis boundary:** This supplement is not a replacement for prescription medication, medical evaluation, lab testing, or disease-specific care. If you have a diagnosed condition, take prescription medication, are pregnant or breastfeeding, or have kidney/liver disease, discuss use with your clinician before starting. **Magnesium-specific cautions:** The adult tolerable upper intake level for supplemental magnesium is 350mg/day unless supervised. Separate magnesium from levothyroxine, tetracycline/fluoroquinolone antibiotics, and bisphosphonates. Avoid unsupervised magnesium supplementation in advanced kidney disease or eGFR below 30 mL/min/1.73m2.