PAREXEL International is a multinational life sciences consulting firm. It conducts clinical trials on behalf of its pharmaceutical clients to expedite the drug approval process. It is the second largest clinical research organization in the world and has helped develop approximately 95% of the 200 top-selling biopharmaceuticals on the market today. The company publishes the annual PAREXEL R&D Statistical Sourcebook, operates the PAREXEL-Academy, and councils all of the top 50 biopharmaceutical and top 30 biotechnology companies.

PAREXEL was founded in 1982 by Josef von Rickenbach and organic chemist Anne B. Sayigh initially to advise Japanese and German firms on how to navigate the FDA approval process. The firm has grown organically over the years and through 40 acquisitions. Josef von Rickenbach is credited with establishing PAREXEL’s culture and practices based on the principles he experienced as a researcher at Schering-Plough in Lucerne, Switzerland.

In 1990, the firm expanded internationally and established new practice areas. By 1999 it had a staff of 4,500 and 45 offices. In the 2000s, it grew to over 18,000 employees. PAREXEL’s consulting and clinical trial work has helped establish many household drug brands and contributed to numerous successes in modern pharmacology.

In 2016, the company allied with EMC Corporation to provide a suite of regulated information and content management services. The company has announced that it will be acquired by private equity firm Pamplona Capital Management for approximately $5.0 billion. The deal is expected to close by the end of 2017.

In March 2006, a PAREXEL-run trial on behalf of TeGenero, the now bankrupt German biotechnology firm, on its anti-inflammatory drug TGN1412 to treat rheumatoid arthritis, multiple sclerosis or leukaemia, caused severe inflammation and multiple organ failure in six healthy volunteers at a facility based at Northwick Park Hospital in London. The drug had been tested on animals but this was the first test on humans.

PAREXEL became the target of legal proceedings from lawyers representing the injured volunteers after the insurance policy of TeGenero was unable to provide sufficient compensation. When the liable company subsequently declared bankruptcy, lawyers for the volunteers initiated legal proceeding against PAREXEL and the two parties later entered into talks; the results of this meeting have not been made public.

A documentary shown in the UK on 28 September 2006 featuring journalist Brian Deer as part of Channel 4's Dispatches series exposed uncertainty about the existence of data that should mandatorily have been submitted by TeGenero to the Medicines and Healthcare products Regulatory Agency (MHRA) prior to the trial indicating whether TGN1412 had been adequately tested on human blood in vitro. Concerns were also raised about whether a safe human dosage was properly obtained by TeGenero. The MHRA however concluded that none of the companies involved could be held responsible for the outcome of the test and that the adverse events that occurred were most likely caused by an unpredicted biological action of the drug in humans.