Mesotherapy is a form of treatment that involves injecting tiny amounts of a substance into the mesoderm, which is the layer of fat and connective tissue directly below the skin. It is thought that the injection of certain substances can either dissolve underlying fat, or cause healing by other mechanisms. Mesotherapy has been used in France and other European countries since the middle of the 20th century to treat conditions such as obesity, hair loss, sports injuries, and certain diseases of the circulation. It has only recently caught on in the US as a form of treatment for cellulite and localized fat.

The exact substance injected under the skin depends on what condition is being treated. Natural compounds, synthetic drugs, local anesthetics, and vitamins may be injected; these are thought to dissolve underlying fat and thereby cause weight loss. A tiny needle is used to inject the substance, making this a less painful treatment than conventional injections with larger needles. Multiple treatment sessions are usually needed. A single session may cost up to $600 or more, and may include special diet and exercise plans.

At present, Mesotherapy is considered a form of alternative medicine in the United States, and is somewhat controversial. Mesotherapy practitioners and patients often claim excellent weight loss results in as little as four or five treatment sessions. However, Mesotherapy treatments are empiric, and currently lack concrete scientific evidence of how exactly they work. Critics of Mesotherapy are unsure whether the weight loss reported by advocates is attributable to the treatment itself or to lifestyle changes.

In the US, the practice of Mesotherapy is largely restricted to trained and licensed physicians, such as plastic surgeons. However, no license is currently required to be a mesotherapist. It is therefore important for anyone considering Mesotherapy to find out what substance is being injected, how many treatments are required, and what potential side effects may occur.