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Amgen Halts GDNF Trial: What’s All the Controversy About?

*(Originally published on this website in February 2005; Updated September 2005)

Amgen’s abrupt halt of its Phase II GDNF (glial cell derived neurotrophic factor) trial in September 2004 has sparked a controversy pitting patients’ willingness to accept risks to obtain a promising new treatment against the “cold logic of science and business.”  A year later the controversy continues. At the center of the controversy are issues that can play out in any clinical trial:

  • Compassionate Use — Is a company obligated to continue supplying an experimental drug to its clinical trial patients, even after it stops developing the drug for safety and/or efficacy reasons? For criteria used to determine if Compassionate Use guidelines apply, see Expanded Access to Experimental Therapies Should patients have a say as to how much risk they are willing to assume to achieve potential benefits? For more information on risks and benefits of clinical trials see:  "Medical Progress Requires Calculated Risks."

  • What criteria should be used to determine the “success” and “failure” of treatments at this phase of development?

  • “Placebo Effect” —  Some studies Parkinson's trial halted : Nature News save suggested that anticipation of treatment can induce a patient's brain to produce more dopamine, which alleviates PD symptoms. This could explain why some clinical trial participants show improvement after receiving a placebo. For more information on this phenomenon, see "Placebo Effect in Parkinson's," and "The Healing Power of Placebos" on the FDA website.

  • Informed Consent — There is an ethical as well as a legal responsibility to ensure that individuals both consent to and understand their participation in clinical trials. What specific information must the research team give potential participants before they decide whether or not to sign the informed consent document? Plaintiffs in the case against Amgen learned that informed consent is not a contract.  (see Informed Consent or visit: the Code of Federal Regulations Requirements for Informed Consent page, or the Office for Human Research Protections website.

Amgen stated in September 2004 that concerns about safety and a lack of efficacy prompted the company to halt the trial after six months and withdraw the drug from all participants. Many trial doctors, researchers, and patients vehemently disagreed with Amgen’s findings, and continue to advocate that GDNF be made available to those who want to continue the treatment.

To learn about the varying positions in the GDNF controversy taken by the trial participants, trial doctors, Parkinson's Organizations, the grassroots and Amgen in the GDNF controversy, see: Responses to Trial Halt.

Read an overview of the controversy on this website.

Next Steps
  • Trial doctors plan to ask the FDA to make GDNF available under a "compassionate use" or Treatment IND clause.

  • Amgen said that for the time being, it is willing to provide GDNF for laboratory and animal studies of the safety issues or of alternate delivery methods (e.g. gene therapy or cell transplants).

  • Scientists in other laboratories are developing alternative ways to deliver GDNF into the brain. At Chicago’s Rush University Medical Center, Jeffrey H. Kordower is working with a California biotech company (Ceregene,) to test a gene therapy approach.

  • To promote ongoing GDNF research, the Michael J. Fox Foundation (MJFF) for Parkinson's Research brought together 35 scientists from around the world to brainstorm new ways to reassess the safety and effectiveness of GDNF without human testing. The group agreed on six to eight new experiments to try.

  • MJFF has awarded a Swedish research team $3 million over four years to develop a neuroprotective therapy based on directly implanting into the brain encapsulated cells that produce natural, not synthetic, GDNF. This will help resolve and advance understanding of GDNF's therapeutic potential as well as potential delivery system variables.  

“This project drives forward potentially breakthrough technologies on two fronts,” said Deborah W. Brooks, Executive Director of the Foundation. “First, should encapsulated cell technology prove safe and effective, the result would be a novel delivery mechanism with applications for a myriad of therapies for Parkinson’s patients. In addition, the team will further assess the ability of GDNF to slow, halt or even reverse the degenerative effects of Parkinson’s disease.” 

The end of the trial devastated Richard Hembrough who, after two years on GDNF in Britain, regained the ability to smell, walk and talk he had lost over the course of his 20-year battle with PD.  

"I worry that my body will regress again, that I will lose the ability to walk and end up in a wheelchair again,” he said. "This drug has given me a new burst of life, and without it I can't help but fear for the worse. But my biggest sadness is for other Parkinson's sufferers. They will miss out on a treatment which could transform their lives. I'm the guinea pig, I should know."

Here’s how you can help
  • Visit and tell others about the GDNF 4 PARKINSON'S! website.

  • [no longer online]
  • Write to the patients to offer your support - email  gdnf4parkinsons@yahoo.com [no longer online]

  • Contact the Parkinson's organizations and ask them to advocate for and support compassionate use treatment for these patients.

  • Write to Amgen and tell them why you support the trial participants'
    request for continued treatment.

Address letters to: 

Kevin Sharer
Chairman of the Board, Chief Executive Officer and President

Dr. Roger M. Perlmutter
Executive VIce President, Research and Development

Dr. Joseph Miletich
Senior Vice President, Research and Pre-clinical Development

Amgen Inc.
One Amgen Center Drive
Thousand Oaks, CA 91320-1799

Please also send a copy of your letter to the Parkinson Pipeline
Project at

Individuals who volunteer to participate in clinical trials of pioneering medical research make a major contribution to speeding up the discovery and availability of safer, more effective treatments and, eventually, a cure, for Parkinson’s disease. All of us owe them a debt of gratitude.


(1)  Pollack, Andrew. “Many See Hope in Parkinson's Drug Pulled From Testing.” New York Times, November 26, 2004.

(2) Gardner, Amanda. Trial Halted for Promising Parkinson’s Drug.” WCNC.com website, October 5, 2004. Retrieved online

(3) E-MOVE. Antibodies to GDNF Force Halt to All Clinical Trials.”  E-MOVE reports from the 129th Annual Meeting of the American  Neurological Association, held in Toronto October 2-6, 2004. 

(4) Talan, Jamie. Drug trial – and error?" Newsday, November 22, 2004.

(5) “Amgen's Phase 2 Study of GDNF for Advanced Parkinson's Disease Fails to Meet Primary Endpoint; Six Months of Treatment Showed Biological Effect But No Clinical Improvement” Amgen press release, June 28, 2004.

(6) “Grant to fund development of encapsulated cell delivery of GDNF for Parkinson.” Drug Week, July 30, 2004, Pg. 395.

(7) Leaps Project to Advance Encapsulated Cell Delivery of GDNF. Michael J. Fox Foundation  press release, July 1, 2004. Retrieved online

(8) “Give Us Back Our Miracle Drug.” Bristol United Press / Western Daily Press November 25, 2004, Pg. 18

Related Issues

Placebo Effect

Access to Experimental Treatments

Informed Consent

Kathleen K. Reardon: Wishing Unethical Pharmaceuticals and the Buddies the Nightmares They Deserve (blog) (leaves this website)

Kathleen K. Reardon: Who's Voting for Your Health (blog)  (leaves this website)



Copyright© 2012 Pipeline Project

All rights reserved. Revised: 01/26/12.