Serum l carnitine and vitamin D levels may be low among oral sildenafil citrate non responders International Journal of Impotence Research Do nutraceuticals work in erectile dysfunction? Although nutraceutical based treatments are often offered for erectile dysfunction (ED), their efficacy remains doubtful. In a recent meta analysis, the efficacy of available nutraceutical Siren Labs L Carnitine Elite Burn Liquid Keto Fat Burner and Metabolism Activato Klaire Labs SFI Health L Carnitine Tartrate 500 mg Amino Acid Stabilized L Carnitine No Synthetic D Carnitine 60 Capsules