The United States Food and Drug Administration (FDA) did not allow Elon Musk and his brain-computer interface company Neuralink to test their brain chip implants in humans, Reuters reported.

While the sources declined to give Reuters the FDA's written denial, explaining it was a confidential document, they described the features of the devices that caused the regulator's concerns.

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In explaining its decision, the FDA outlined dozens of safety issues the company must resolve before moving forward.

The agency's major safety concerns involve the battery system of the device, the potential that the tiny wires of the implant could migrate to non-targeted areas of the brain, and questions over how and if the device can be removed without damaging the human brain.

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As noted by Reuters, the FDA rejection does not mean that the company's development is doomed and that it will not be able to obtain permission to conduct human trials. However, it will be much more difficult to do so since this decision by the regulator indicates that it has serious concerns.

In late 2022, Elon Musk announced that the company would receive FDA approval and begin human trials within six months – that is, by the spring of this year.