When to take L carnitine: Dosage, forms, and side effects Taking a preworkout AND carnitine? It is important to get the timing of each supplement right to get the best results with both. Watch as Phil explains the best way to combine them. , #preworkout L Carnitine as Pre Workout Supplement: Guide The Science of Good Health When Should You Take L Carnitine? MuscleTech Should I use L Carnitine on rest days or just before workouts? Combining L Carnitine with Pre Workout for Effective Fat Loss