I use meldonium myself, and it is a good compound if you expect from it the right thing. It will not increase your endurance, but it is very good for the recovery of your cardiovascular system after training hard. Besides, it barely has any side effects at all, and it is rather cheap, so by me it is definitely worth to add it to your supplement stack. Just one use it in excess - 250-500 mgs per day should be plenty.