When Should You Take L Carnitine? MuscleTech Creatine vs Carnitine: Do You Need Both? Differences Explained FeastGood.com How long it takes for creatine to work can depend on your baseline creatine levels, consistency of use, hydration, exercise routine, diet, and age. Creatine monohydrate and L carnitine are two of the most researched supplements in the game., We are talking years. Decades. Proven over and over again., Creatine is your foundation., More strength.