Despite powerful backing for the Right to Try bill, resistance among patient advocacy groups is strong.

Terminally ill patients can be desperate for any treatment that might save their lives. Even if the chances are bleak, it seems worth a shot. That dire need has led Congress to pursue a bill that would allow patients to access experimental drug treatments that bypass the Food and Drug Administration's clinical trial process. But the legislative fight pits President Donald Trump and other powerful conservatives, including the Koch brothers, against many voices from the medical community and patient advocacy organizations.

Trump prodded lawmakers last week to turn the bill, known as "Right to Try," into law. A lawmaker working closely on the issue said the president asked him point blank, "How close are you to getting this done?" Trump previously stressed the importance of the bill in his State of the Union Address.

The Goldwater Institute, a libertarian think tank backed by the Koch brothers, is the main political think tank pushing Right to Try. It already has helped the legislation pass in 38 states.

But resistance among patient advocate groups is strong. Thirty-eight groups wrote a letter to Congress on Feb. 6 arguing that the bill would actually hurt terminally ill patients. The coalition, which includes the American Lung Association and the American Cancer Society Cancer Action Network, said in the letter to Congress that Right to Try would exploit vulnerable patients and allow unethical companies and providers to circumvent the FDA and sell dangerous medicine to desperate people.

"It is important to remember that the current regulatory system for medical products and research in the United States was created as a result of serious patient harm and exploitation that occurred early in the 20th century," the letter states. "Clinical research subject protections are in place when experimental products are being tested to ensure the safe and ethical treatment of research participants."

The FDA already has a system in place to give terminally ill patients access to experimental treatments not approved by the FDA. The system, called compassionate use or expanded access, requires the consent of a doctor and drug company. If the FDA doesn't object to a patient taking the unapproved drug, the patient can do so. The letter points out that the FDA approved 99.7 percent of compassionate-use requests, but supporters of Right to Try believe the approval process takes too long. The FDA states on its website that treatment may begin 30 days after FDA receives an investigational new drug application (IND), or earlier if FDA notifies the treating physician that the expanded access use may begin.

As the Right to Try campaign increased its efforts in recent years, the FDA made moves to streamline the application process for patients and doctors seeking experimental drugs that are outside clinical trials.

"Currently, when unapproved drugs are administered to patients for research purposes, important ethical and safety mechanisms are in place," Alissa Crispino, a spokesperson for the American Cancer Society Cancer Action Network said in an email to CNBC.

This wouldn't be the case if Right to Try became law.

"It removes important safety protections and creates openings for potential bad actors to take advantage of patients," Crispino said.