D-Carnitine is the D-enantiomer of carnitine, which differs from the biologically active L-Carnitine. Unlike L-Carnitine, D-Carnitine does not effectively facilitate fatty acid transport into mitochondria for energy production and may even inhibit L-Carnitine's activity by competing for uptake. As a result, it is not widely used as a supplement in health and fitness applications and can potentially lead to carnitine deficiency if consumed in excess. Instead, D-Carnitine is primarily employed in scientific research to study carnitine metabolism, enantioselectivity in biological systems, and as a reference standard or antagonist in pharmacological studies. It may also find niche applications in biochemical assays or as an intermediate in the synthesis of carnitine derivatives. Due to its limited biological activity, it is not recommended for therapeutic use without specific medical supervision.