I do think there's a lack of really good solid evidence in humans, but that might only be because it's just not studied enough, and that's usually the case
Lancet (2016) 388(10053):1659724
Administration Routes: Choosing the Right Method Vitamin B12 injections can be given in different ways
Each format has trade-offs in absorption and handling for research
How Glutathione Injections Work at Our Naples Clinic Before starting treatment, providers at our Naples clinic follow a structured process focused on medical evaluation, personalized care, and ongoing monitoring
Vidal-Casariego 2013 meta-analysis: Four RCTs with 284 type 2 diabetes patients showed 23 g/day L-carnitine for 1252 weeks reduced fasting glucose, total cholesterol, LDL cholesterol, and apolipoproteins B100 and A1 but NOT triglycerides, lipoprotein(a), or HbA1c [3][43]