I've tried all forms of magnesium with vyvanse and adderall. The issue for me, is that I was deficient in both calcium and magnesium (according to blood tests). Taking magnesium without balancing it with calcium intake messed me up. Nowadays I have a source of calcium in the morning, and magnesium at night.

If you're low on calcium, then taking magnesium will cause a huge inhibition of excitatory firing, which will dampen the effects of stimulants. This protects your brain, but also makes the stimulants feel dull. It's a double edged sword.

Although stimulants primarily target dopamine release, part of what makes stimulants work so well, is the serotonin release, which gives you a sense of well being. If you dampen the action of the stimulants, you can end up feeling flat (unmotivated with no sense of well being) and that can make you anxious.