Hundreds of drugs have been in short supply in recent years, including many to treat cancer.
Researchers at the University of Pennsylvania School of Medicine surveyed nearly 250 oncologists and found 83 percent of doctors said they have faced drug shortages.
"Our survey found that thousands of patients have had their treatment regimens changed because of drug shortages," said Dr. Keerthi Gogineni with Penn's Abramson Cancer Center.
Forty-three percent of doctors had to delay their patients' treatment and 37 percent had to choose among patients who needed a particular drug.
"They need to prioritize when there is limited drug availability. These decisions are fraught with ethical complications," Dr. Gogineni said.
Previous research from last December found a link between drug shortages and higher rates of relapse in lymphoma patients like Abby Alonzo -- she was forced to switch medication right in the middle of her treatment.
"At 12 weeks, when we went back for the radiation, we had seen she had relapsed," said Katie Alonzo, Abby's mother.
Problems with quality and manufacturing are behind many drug shortages in the U.S. But since last year, manufacturers are required to notify the FDA of shortage problems. The agency says it's been able to lower the number of drug shortages and also prevent some from happening.
Vinita Nair - CBS News