Doctors in West Texas are seeing measles patients whose illnesses have been complicated by an alternative therapy endorsed by vaccine skeptics including Robert F. Kennedy Jr., the health secretary.

Parents in Gaines County, Texas, the center of a raging measles outbreak, have increasingly turned to supplements and unproven treatments to protect their children, many of whom are unvaccinated, against the virus.

One of those supplements is vitamin A, which Mr. Kennedy has promoted as a near miraculous cure for measles. Physicians at Covenant Children’s Hospital in Lubbock, Texas, say they’ve now treated a handful of children who were given so much vitamin A that they had signs of liver damage.

Some of them had received unsafe doses of supplements for several weeks in an attempt to prevent a measles infection, said Dr. Summer Davies, who cares for acutely ill children at the hospital.

“I had a patient that was only sick a couple of days, four or five days, but had been taking it for like three weeks,” Dr. Davies said.

While doctors sometimes administer high doses of vitamin A in a hospital to manage severe measles, experts do not recommend taking it without physician supervision. Vitamin A is not an effective way to prevent measles; however, two doses of the measles, mumps and rubella vaccine are about 97 percent effective.