The National Institutes of Health (NIH) today detailed how President Donald Trump’s administration will implement restrictions it announced in June on the use of human fetal tissue in research. For some researchers, the announcement brings relief: The policy doesn’t kick in immediately, meaning grant applications already in the pipeline at NIH won’t be affected. But starting in late September, scientists applying for grants will need to explain in detail why they need to use fetal tissue and how it will be obtained.

The new paperwork requirements, along with a new, lengthy ethics review, raise worries that many investigators will fail to land grants that rely on fetal tissue—and others won’t even try to win them. “With these rules, it’s not impossible” to do fetal tissue research with NIH support, says Lawrence Goldstein, a stem cell neuroscientist at the University of California (UC), San Diego, “but it’s going to be very problematic.”

“This does a pretty good job of doing what the pro-life people want. It makes grant applications a lot more onerous, substantially and procedurally, while allowing [the Trump administration] to say: ‘We’re not completely banning it,’” says Hank Greely, a bioethicist at Stanford University in Palo Alto, California.

But David Prentice, vice president and research director at the antiabortion Charlotte Lozier Institute in Arlington, Virginia, defends the new rules: “The language is trying to hold an ethical standard for the research proposals and the research that might be done. The policy is not just about science. It’s also about ethics.”

Abortion rights opponents oppose fetal tissue research because it uses tissue donated by women who have had elective abortions. (The tissue would otherwise be discarded.) In September 2018, the Department of Health and Human Services (HHS) launched a review of federally funded research with the tissue, which researchers argue is essential for studies in areas such as HIV and other infectious diseases, eye diseases, and fetal development. In 2018, the agency spent about $115 million on roughly 173 projects that use fetal tissue.

On 5 June, that review concluded, and HHS announced a strict new policy . It banned any fetal tissue studies by in-house NIH scientists and said that proposals from outside scientists that NIH greenlights for funding must next go through an ethics review lasting up to 6 months. The review will be performed by a new kind of panel: an Ethics Advisory Board appointed by the HHS secretary. ( The board of 14–20 people must include a theologian, an ethicist, and an attorney; no more than half its members can be scientists.)

Today’s announcement fleshes out the requirements for extramural grant and contract proposals submitted on or after 25 September. In their proposals, applicants will need to describe the process they will use to obtain consent to use tissue from a woman having an abortion. (Until now, a university official simply needed to certify that the tissue would be obtained in accordance with federal ethics regulations.) Applicants will also have to explain how they will dispose of the tissue. They will also need to provide scientific justification for not using an alternative such as adult tissue or organoids. And, for NIH’s mainstay “R01” proposals, they will need to do this within the 12-page limit of the “research strategy” section. The space crunch “is going to detract from the scientific plan,” Goldstein says.

Heather Pierce, senior director of science policy and regulatory counsel at the Association of American Medical Colleges in Washington, D.C., worries the space constraints alone may discourage scientists from trying to use fetal tissue at a time when competition for NIH grants is already intense, regardless of research area. “ In the context of a chilling effect, that’s space that you can’t use to describe your science.”

Many scientists who read the policy also interpreted it to forbid the use of fetal tissue by young scientists on the salary-supporting training grants and fellowships that help graduate students and postdocs. That is incorrect, NIH later clarified. Trainees will be free to work on fetal tissue research that has passed muster under the new regime, says NIH spokesperson Renate Myles.

The policy also bans NIH funding for work with cell lines created from aborted fetal tissue after 5 June, the day that the new Trump administration policy was announced. Deepak Srivastava, a stem cell biologist who is president of the International Society for Stem Cell Research and the president of the Gladstone Institutes in San Francisco, California, says he was pleased by the grandfathering in of preexisting cell lines. But, he adds: “Creating unnecessary hurdles and roadblocks to ongoing fetal tissue research doesn’t recognize fully the ongoing need—despite current technologies—for fetal tissue research to continue to make medical advances for human health.”

Some researchers say they are removing fetal tissue from their proposals to avoid jeopardizing the overall project, even if it means jettisoning years of work. Warner Greene, an HIV scientist at the Gladstone Center for HIV Cure Research in San Francisco, says he is taking initial steps to move his research for an HIV cure from humanized mice to monkeys—even though monkeys can’t be infected with human HIV, and instead he must use an analogous, monkey-infecting virus—and even though a new president could reverse the Trump policy in 2021. One of his experiments relying on mice created using human fetal tissue has already been scuttled by the new policy, he notes, and he does not want to get burned again. “It just makes no sense to start an experiment not sure you can finish.”

*Clarification, 29 July, 6:15 p.m.: Many scientists, and the original version of this story, interpreted the NIH notice as forbidding the use of fetal tissue by young scientists with training grants or fellowships. The notice states that “Training awards and individual fellowships may not propose research using [human fetal tissue].” However, in a 29 July statement, NIH clarified that, “Since training and fellowship grants are not research grants, they will not be affected by the policy. Trainees or fellows can still conduct fetal tissue research if it’s part of an approved research grant that meets the policy requirements and receives approval by an ethics advisory board.”

*Clarification, 6 August, 10:35 a.m.: NIH today published its own clarification of the language pertaining to trainees that appeared in its initial notice. The agency writes: “Trainees and fellows may not independently propose research using [human fetal tissue]. However, trainees and fellows can still conduct [human fetal tissue] research if it is part of a mentor or sponsor’s award and meets all policy requirements.”