along with tachycardia all day long. I've been taking gabapentin for about 3 weeks. I know I've got a faster heart beat than normal but this is ridiculous. A friend suggested I buy an oximeter to check my oxygen level and found out about the bad tachycardia. It can hit l40 BPM but usually is around ll7. Dr. told me to cut gabapentin in half which I'm doing. But I did a search and find that lack of magnesium will bring on both of these. I've been taking 600 mg. magnesium citrate daily for about 4 days. My question is how long does it take for magnesium to kick in? Should I also be taking calcium and potassium? I'm also starting to take some molasses in milk thinking this might get into be faster.