If you're a young man who already eats enough protein and works out with weights, taking extra leucine won't help your muscles grow any more — your muscles just can't use more than a certain amount, no matter how much you give them.

If you're a young man who lifts weights regularly, eating 1.8 grams of protein per kilogram of your body weight every day is enough to build as much muscle as you can from training—adding extra leucine powder won't help you get any bigger or stronger.

Taking extra leucine pills won’t help you build more muscle, get stronger, or recover faster from weight training if you’re already eating enough protein.

Taking extra leucine — a supplement found in protein — won’t help healthy, fit young adults build more muscle, get stronger, or recover faster from workouts, no matter how much they take or how long they take it, for up to 12 weeks.

Taking leucine supplements won't help you get stronger when you're already trained and lifting weights for 8 to 12 weeks.

If you're a young guy who lifts weights and already eats enough protein, taking extra leucine pills for 12 weeks won't make you stronger or build more muscle in your thighs than just lifting weights by itself.