The Food and Drug Administration has suspended experiments on the effects of nicotine in squirrel monkeys, research aimed at better understanding one of the most pernicious of addictions.

Two weeks ago, British primatologist Jane Goodall wrote to FDA Commissioner Scott Gottlieb, urging an end to what she called “cruel and unnecessary” and “shameful” research.

On Monday, he responded, saying that he had put a hold on the study this month “after learning of concerns related to the study you referenced.” He also said he has sent a medical team of primate experts to the FDA facility — the National Center for Toxicological Research in Arkansas — “to evaluate the safety and well-being of the monkeys and to understand whether there are additional precautions needed.”

The research involved training adolescent and adult squirrel monkeys to press a lever to give themselves infusions of nicotine. Four monkeys in the studies, which began in 2014, have died, according to people close to the situation. The deaths are still being investigated, but nicotine overdose isn't seen as the likely cause.

Gottlieb also told Goodall that he has appointed an FDA team, including senior career officials and guided by primate veterinarians, to assess the “science and integrity” of the animal research process for the study and whether the research should be resumed. If the study is terminated, he said, the monkeys will be sent to an alternative location that can provide appropriate long-term care.

An FDA spokeswoman said the agency is also considering creating a wider-ranging “function that would provide for even greater oversight of the care of animals in the agency’s possession.”

The FDA actions represent the latest change in how the federal government treats research animals. In 2015, the National Institutes of Health said it would no longer support biomedical research on chimpanzees. The Department of Veterans Affairs said Monday that it would step up its oversight of experiments on dogs after an investigation found canine deaths at a Virginia research facility, USA Today reported.

Goodall was enlisted in the fight against the monkey tests by the White Coat Waste Project, an advocacy group that says its goal is to publicize and end taxpayer-funded animal experiments. In January, the organization obtained 64 pages of documents on the nicotine-addiction research from the FDA under the Freedom of Information Act. It is suing the agency to get more information on the research's costs, as well as veterinary records and photographs and videos of the experiments.

Based on a brief description on the agency's website and the FOIA documents, the experiments appeared to involve 12 adolescent and 12 adult monkeys.  The goal was “to examine behavioral and biological effects of nicotine in squirrel monkeys,” comparing the two age groups, the website said. The idea seemed to be to get the monkeys addicted to nicotine and then to see how they reacted to decreasing levels of the drug.

“Characterizing the effects of decreasing doses of nicotine on rates of self-administration in a nonhuman primate species will provide valuable information to inform what we might expect in human users when nicotine levels in tobacco products are lowered,” said one of the documents obtained by the White Coat Waste Project. Another document noted that “further information regarding the role of nicotine dose in the onset and maintenance of tobacco product use, particularly during adolescence, would be useful.”

Under federal law, the FDA has the authority to lower nicotine in cigarettes, and officials have long talked about it. In July, Gottlieb said he wanted to curb smoking by lowering the nicotine level in cigarettes to nonaddictive levels.

On Monday, in writing to Goodall, Gottlieb noted that he was committed to reducing the agency's reliance on animal studies through the increased used of “in vitro” tests and computer models.

Both the Jane Goodall Institute and the White Coat Waste Project praised his suspension of the experiments. The institute, based in Vienna, Va., called the action “a profoundly positive development” and praised Gottlieb's stated commitment to “alternative and more efficient approaches replacing invasive animal testing for this and many other kinds of research.”

Justin Goodman, vice president for advocacy and public policy at White Coat Waste Project, lauded Gottlieb “for taking swift and decisive action to suspend and scrutinize this wasteful and secretive project.”

But the FDA, whose animal research involves not only monkeys but also mice, rats, frogs and fish, is unlikely to abandon animal research, which is used to support its regulatory decisions. In his letter, Gottlieb noted that “currently there are some areas for which non-animal testing is not yet a scientifically valid and available option.”

For example, nonhuman primates are the “most appropriate animal model” for studies on the bacteria that causes whooping cough because of the biological similarities to humans, officials said. Monkeys also are used in research on Creutzfeldt-Jakob disease, a rare, degenerative brain disorder.

Some scientists took issue with Goodall's criticism of the FDA monkey research. In an open letter on the  website, scientists from institutions such as the Johns Hopkins University School of Medicine, Harvard Medical School and Wake Forest School of Medicine, disputed her assertions that “the results of smoking are well-known in humans” and that the same research could be conducted in people rather than monkeys.

With more than 440,000 people in the United States dying from tobacco use each year, the scientists said, “clearly nicotine addiction remains a significant public health problem and it is quite evident that we do not understand this disorder well enough to eradicate it.” They added, “Addiction is a major public health issue worldwide, and requires and deserves close scientific scrutiny, some of which will require the use of animals.”

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