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.

Taking leucine supplements won’t make you stronger in the gym if you’re already a healthy, trained young adult lifting weights—even if you take up to 5 grams a day for a couple of months.

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 leucine supplements won't help healthy, trained young adults recover faster after a tough workout, based on how sore they feel, how much strength they lose, and a blood marker for muscle damage.

Taking leucine supplements won't help you recover faster from tough workouts if you're already fit and healthy — your muscles will bounce back just as well with a fake pill.