This 2020 review subject was carnitine, acetyl-L-carnitine, and its other molecular forms:

“Carnitine is necessary to deliver long-chain fatty acids from cytosol into mitochondria. Carnitine homeostasis is maintained by diet and renal absorption, as only a small amount (about 25%) is obtained by endogenous biosynthesis.

Defective fatty acid oxidation occurs with reduced intracellular levels of carnitine, leading to glucose consumption instead of lipid consumption, resulting in hypoglycemia. Non-metabolized lipids accumulate in tissues such as heart, skeletal muscle, and liver, resulting in myopathy and hepatic steatosis.

2000 mg/day is unlikely to provoke unwanted side effects and is safe for humans. In-depth studies are needed to identify a unique method of analysis which can guarantee efficient monitoring of supplement active component amounts.”

https://www.mdpi.com/1420-3049/25/9/2127/htm “The Nutraceutical Value of Carnitine and Its Use in Dietary Supplements”

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The review listed animal studies of L-carnitine alone and in combination with:

• Vitamin D3;
• Coenzyme Q₁₀;
• Nicotinamide riboside;
• Selenium;
• L-arginine;
• Anti-histamine drugs cetirizine hydrochloride and chlorpheniramine maleate; and
• Hypertension drug olmesartan.

Human studies of its effects included:

• Muscle soreness, damage biomarkers, and cramps;
• Osteoarthritis knee pain and inflammation markers;
• Ischemic cerebrovascular injury;
• Peripheral neuropathy;
• Nonalcoholic fatty liver disease;
• Insulin resistance and Type 2 diabetes;
• Kidney diseases;
• Inherited diseases phenylketonuria and maple syrup urine;
• Stress, depression, and anxiety;
• Male infertility; and
• Hepatitis C.

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