I have taken magnesium for years. I take SlowMag (143 mg magnesium chloride) in the morning and Magtein (1000 mg magnesium l-threonate) at bedtime. SlowMag has no ill effects. Magtein takes some getting used to, but now makes me sleep like a baby.

When I started Magtein, I would go right to sleep but wake up 4 hours later. After going back to sleep, I would feel groggy in the morning. It took about a month to get over both side effects.