L Carnitine Force Factor ALCAR Supplement for Cognitive Function and Stamina L Carnitine injection is recommended at 1 ampule every 2 3 days for best results. The L Carnitine is taken intravenously either by normal injection or using a butterfly needle. After taking this L Carnitine, you Benefits of Combining Supplements: L Carnitine & Methyl B 12: The Center for Internal and Integrative Medicine: Integrative Medicine Doctors