Lipoic (thioctic) acid (LA) [R-5-(1,2-dithiolan-3-yl)pentanoic acid] is a natural compound that enters the human body with food. LA is used to treat many diseases such as diabetes, multiple sclerosis, Alzheimer’s and Parkinson’s diseases, liver disease, obesity, and others. It is also used as an antidote for intoxication with heavy-metal and various toxins. LA causes phosphorylation of insulin receptors and modulates 5’-AMP-activated protein kinase (AMPK) levels in tissues. LA triggers expression of many proteins of the antioxidant response. Pharmacological application of LA reduces the levels of C-reactive proteins and triglycerides and improves the indices of glycemia and inflammation biomarkers. The safety level of LA is considered well studied. However, data on the need for a more thorough approach to the composition of LA preparations and for the determination of LA concentrations and the duration of treatment are being accumulated. The present review considers the possibility of side effects depending on the duration of treatment and LA concentration and various areas of application of improved LA modifications, including nanosized forms.