Magnesium closes a common intake gap; some salts loosen stool. Strongest signal is a small blood-pressure drop, clearer with high pressure or low magnesium. Blood-sugar and inflammation move favorably. Sleep and mood evidence is mixed. Night cramps in older adults are not supported. Loose stools limit the dose. High blood magnesium is mainly a problem when kidneys cannot clear it. (Full Review)

Protocol

Common longevity range

200–400 mg/day elemental

On top of food, staying near the 350 mg supplemental upper level unless laxation is intended

Single versus split

100–200 mg elemental two or three times daily

Improves absorption and limits diarrhea versus one large evening load

Time of day

Evening or split morning/evening

Evening when sleep is the target; split when the target is body stores or blood pressure

Time to effect

Blood pressure

4–12 weeks

Measured in trials; more visible when pressure is high or magnesium is already low

Bowel effects

Within a day

Osmotic laxative effect of poorly absorbed salts such as oxide and citrate

Glucose handling

4–12 weeks

Measured in trials in type 2 diabetes and high diabetes risk

Benefits

High: Modest blood pressure reduction; Relief of functional constipation

Medium: Improved glucose handling; Lower circulating C-reactive protein; Migraine frequency reduction

Low: Sleep quality; Depressive and anxiety symptoms; Premenstrual symptom relief; Hip bone mineral density; Idiopathic muscle cramps; Restless legs symptoms; Lower post-exercise muscle soreness

Speculative: Cognitive performance with magnesium L-Threonate; Lower death rates from food, not supplements

Contraindications

Advanced chronic kidney disease (eGFR <30 mL/min/1.73 m²) unless a clinician is targeting and monitoring serum magnesium

Documented hypermagnesemia

Complete heart block without a pacemaker, at high or intravenous doses

Myasthenia gravis, especially injected (parenteral) magnesium

Known bowel obstruction (oxide at gram-level doses)

Key Interactions

Bisphosphonates (alendronate, risedronate): separate ≥2 hours

Tetracyclines (doxycycline) and fluoroquinolones (ciprofloxacin): take magnesium 2 hours before or 4–6 hours after

Levothyroxine: separate 4 hours

Gabapentin: separate ≥2 hours

Sotalol: separate 2 hours

PPIs (proton-pump inhibitors; omeprazole, esomeprazole, pantoprazole): magnesium loss after months to years

Loop and thiazide diuretics (furosemide, hydrochlorothiazide): renal magnesium wasting; potassium-sparing agents (spironolactone, amiloride) can raise magnesium

Calcium-channel blockers (amlodipine, verapamil) and other antihypertensives: additive blood-pressure lowering

Potassium and other blood-pressure-lowering supplements (CoQ10, coenzyme Q10; garlic): additive vasodilating effect

Calcium supplements: compete for absorption

Vitamin D: bidirectional effects on 25-hydroxyvitamin D

High-dose zinc: stagger or avoid long concurrent use

Magnesium-containing antacids and laxatives (milk of magnesia, magnesium citrate): additive osmotic load and hypermagnesemia risk, especially in low eGFR

Digoxin: low magnesium increases arrhythmia risk

Risk & Side Effects

High: Gastrointestinal upset and diarrhea; Hypermagnesemia when kidneys cannot excrete the load

Medium: Impaired absorption of other oral drugs; Additive blood-pressure lowering

Low: Secondary electrolyte shifts

Speculative: High serum magnesium and cognition

Monitoring

Marker	Target	Why
Serum magnesium	2.0–2.5 mg/dL (≈0.82–1.03 mmol/L)	Screens deficit and toxicity
Red-blood-cell magnesium	5.0–6.5 mg/dL	Closer to tissue stores than serum
24-hour urine magnesium	Rise toward ~3–5 mmol/day on a stable dose	Confirms absorption and intake
eGFR	≥60 mL/min/1.73 m² before unsupervised high-dose use	Safety gate for accumulation
Sitting blood pressure	Track change from seated baseline	Tracks the strongest clinical signal
Fasting glucose or hemoglobin A1c	Change from the person's baseline	Tracks metabolic response
High-sensitivity CRP	<1.0 mg/L as a general functional target	Optional inflammation marker

Cadence: 8–12 weeks after a stable dose, then every 6–12 months; earlier if eGFR is reduced or high-dose oxide or citrate is used as a laxative

Qualitative Assessment

Stool form (Bristol scale): loose stools mean the osmotic ceiling has been reached
Sleep latency and nocturnal awakenings, if those were the reason for an evening salt
Resting muscle tightness, palpitations, and migraine days, tracked against the person's own baseline
Energy on ordinary training days, without expecting a performance drug effect

Magnesium for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment