The recommended dose is 3 per day (the zma I’m using right now). Which has 450 mg. magnesium and 30 mg zinc and 10.5 mg B-6.
If you aren’t doing workouts regularly, you may consider taking half this dosage.
It certainly worked for me: I feel much less fatigue compared to the past since I started to use zma. My body recovers faster after the workouts- it’s really good stuff.
To compare different brands, you should consider the amount of nutrients inside them. The dosages I mentioned above are for someone who works really well for at least 3-4 days a week, I think. (both PE and BB wise).
Good luck.
Start: 6.9 BPEL x 4.9 (17,5 x 12,5 cm)
Now: 7.7 BPEL x 5.7 (19,5 x 14,5 cm)