Immunotherapy has rightly been hailed as a way of treating cancer, enhancing the immune system, instead of weakening it, as chemotherapy does. But there’s a dark side to immunotherapy that doesn’t get much attention, the New York Times reports.

Immunotherapy causes the body to attack the cancer but it doesn’t stop there in some cases. It also turns on healthy tissue in the pancreas, kidneys, bowel, liver, lungs, and heart. These are life-threatening developments that force physicians to weigh the benefits of these “miracle drugs.”

“We’ve heard about immunotherapy as God’s gift, the chosen elixir, the cure for cancer,” John Timmerman, an oncologist and immunotherapy researcher at the University of California, Los Angeles, told the Times. “We haven’t heard much about the collateral damage.”

Timmerman knows this all too well. He recently treated a woman with immunotherapy that “melted away” her cancer. Then, suddenly some weeks later, she got severe cold and flu-like symptoms and died in the emergency department.

The treatments also cause acute-onset diabetes in some patients, and other side effects are starting to get noticed as well.

Most patients do not suffer from severe reactions and, so the thinking goes, let patients deal with arthritis, hepatitis, and diabetes if the alternative is dying from cancer. But often the side effects catch providers off-guard—and not always because they (the side effects) move quickly.

The drugs are so new that many of the side effects have not been noticed, the Times reports.

They appear randomly, often months after treatment and can seem harmless at first. In addition, combo immunotherapy treatments are beginning to be used, and they can increase the risk.

Immunotherapy is moving quickly from clinical trials to hospitals, even hospitals in smaller cities where clinicians may not be as familiar with the risks. While patients’ health is a concern, another one is cost: Some immunotherapy drugs are priced at $250,000 or more per regimen.

William Murphy, of the University of California, Davis, reviews immunotherapy grant requests for the government. He tells the Times that more research needs to be done about the risks.

This comes at a time when pressure mounts on the FDA to come up with a faster approval process.

The recently passed 21st Century Cures Act would speed FDA approval for drugs and medical devices. Opponents argued, to no avail, that the law lowers safety and efficacy standards and contend that the FDA already moves faster than similar agencies in other countries.