Injectable L carnitine works better than oral because it goes straight into your bloodstream, giving almost 100% of absorption versus only 518% with capsules or liquid. Oral L carnitine can take upto 4 LCarnitine Research & Benefits Studies & Scientific Use PDF) Comparison of pharmacokinetics of L carnitine, Acetyl L carnitine and Propionyl Lcarnitine after single oral administration of L carnitine in healthy volunteers L Carnitine Injection Levocarnitine IV L Carnitine Linus Pauling Institute Oregon State University Enhanced Bioavailability of L Carnitine After Painless Intradermal Delivery vs. Oral Administration in Rats Pharmaceutical Research Springer Nature Link