why doesnt dog food contain taurine and l-carnitine is an important amino acid for many functions in the body.⁠, ⁠, There are no known side effects of excess taurine in dogs cats. The only bad thing about taurine is its deficiency. If you reduce oxidative stress L-Carnitine for Dogs & Cats:

Heritability estimates range between 30 and 50%, although genome-wide study results have been inconclusive (Meier et al., 2019)

Markers and Biomarkers of Endothelium: When Something Is Rotten in the State

Br J Clin Pharmacol 2000

Temporary Issues: If the deficiency was due to a temporary medication or a resolved medical condition, the need for shots might eventually cease once the underlying problem is gone and oral absorption is restored

Chen S, Chang C, Deng Y, An S, Dong YH, Zhou J, Zhang LH (2014) Fenpropathrin biodegradation pathway in Bacillus sp

It can also interfere with how your body absorbs nutrients, potentially leading to malnutrition or unintentional weight loss