Three randomized trials covering 151 older adults with Insomnia found oral magnesium helped participants fall asleep about 17 minutes faster than placebo; total sleep rose about 16 minutes, though that gain was not statistically conclusive.
One to two weeks of regular use—not minutes—was the typical window for noticeable sleep benefits, because magnesium acts as a nutrient supporting nerve and muscle function rather than as a sedative.
The evidence remained low quality, with small trials and higher risk of bias, and researchers said the biological link between magnesium and better sleep is still not fully mapped, especially in people without deficiency.
350 mg a day is the adult upper limit from supplements and medications unless a clinician advises otherwise; higher doses can cause diarrhea and interact with antibiotics, osteoporosis drugs, Diuretics and acid reducers.