Medifast, Inc. is an American nutrition and weight loss company based in Owings Mills, Maryland. The company owns five subsidiaries: Jason Pharmaceuticals, Inc. (Jason), Take Shape for Life, Inc. (TSFL), Jason Enterprises, Inc., Jason Properties, LLC and Seven Crondall, LLC. Medifast produces, distributes, and sells weight loss and other health-related products through websites, multi-level marketing, telemarketing, franchised weight loss clinics, and medical professionals.

The company is public with a market capitalization of $405 million, as of October 2014.

Medifast was founded in 1980 by William Vitale, a medical doctor. His products were sold directly to other doctors, who in turn prescribed them to their patients.

The company is publicly traded on the New York Stock Exchange (symbol: MED).

On July 17, 1995, HealthRite (predecessor of Medifast) changed its name from Vitamin Specialties Corp.

In October 2010, Medifast was ranked number 1 on Forbes magazine's list of "America's 100 Best Small Companies". The company was ranked 18th as of the 2014 list.

In September 2012, Medifast's subsidiary, Jason Pharmaceuticals, paid a $3.7 million USD civil penalty for false advertising. The Federal Trade Commission and United States Department of Justice said that advertisements for the "Medifast 5 & 1 Plan" low-calorie diet told consumers they could "lose up to 2-5 pounds per week.", and that these weight-loss claims lacked a reasonable scientific basis, and were unsubstantiated. Under the settlement, any future claims made by the company must be backed by at least one human clinical study.