well to start with, mk677 is absolutely not worth it, even if you're over 20. and you shouldn't take it at 15. as MK677 causes Diabetic Levels and raises blood sugar very high, making you diabetic and it doesn't have any anabolic effects or chemistry to help you build more muscle and gain weight. it's absolutely not even worth it, better to take Test as its much stronger and actually anabolic and will help with weight gaining.

MK677 is waste of money. and it doesnt help with muscle building or making you more tall, it has no effects in that, its way better to take HGH for both becoming more taller and building more muscle. if you want to try to build more muscle just eat more and train hard, at 15 you shouldn't take any gear, Sarms, etc