L Carnitine Is it Worth Taking? Ideal Nutrition Carnitine: the claims and why it may not work L carnitine supplements bioavailability is very less and according to some studies it takes 8 to 12 weeks for for loss results, so if you decide to supplement with oral L carnitine do take it in Frontiers L carnitine prevents lenvatinib induced muscle toxicity without impairment of the anti angiogenic efficacy