Millions of Americans are missing out on a chance to avoid debilitating fractures from weakened bones, researchers say, because they are terrified of exceedingly rare side effects from drugs that can help them.

Reports of the drugs’ causing jawbones to rot and thighbones to snap in two have shaken many osteoporosis patients so much that they say they would rather take their chances with the disease. Use of the most commonly prescribed osteoporosis drugs fell by 50 percent from 2008 to 2012, according to a recent paper, and doctors say the trend is continuing.

Last month, three professional groups — the American Society for Bone and Mineral Research, the National Osteoporosis Foundation and the National Bone Health Alliance — put out an urgent call for doctors to be more aggressive in treating patients at high risk, and for patients to be more aware of the need for treatment. It followed a flurry of recent articles in medical journals documenting and bemoaning patients’ abandonment of traditional osteoporosis drugs. But osteoporosis experts are afraid their efforts will do little to change minds.

“Ninety percent of patients, when you talk to them about starting one of these drugs, won’t go on,” said Dr. Paul D. Miller, medical director of the Colorado Center for Bone Research, a medical practice in Lakewood. “Ninety percent who are on the drugs want to come off. The fear factor is huge.”