Frances Oldham Kelsey has been described as a hero, and for good reason. The Canadian-born doctor saved the U.S. from thalidomide – the dangerous drug that caused thousands of babies to be born with malformed limbs and countless more miscarriages.

Thalidomide was being used during the 1950s in Europe to treat insomnia and morning sickness in pregnant women. But when the drug reached the Food and Drug Administration in September 1960, Frances Kelsey – the new medical officer – was skeptical about its safety. Kelsey requested further information from the manufacturer and, despite significant pressure and complaints, persevered with her enquiry.

Her persistence paid off as evidence against thalidomide began pouring in. Thousands of babies whose mothers took the drug were born with flipper-like arms and legs, missing limbs and organs and other birth defects. Kelsey's refusal to approve thalidomide saved countless children from being born with birth defects associated with the drug. A number of lawsuits have been filed against thalidomide worldwide, which include recent bids from victims for compensation from manufacturers.

Kelsey, who died on Friday at the age of 101, helped improve the regulatory procedure for approving pharmaceutical drugs. CBC Canada reports that while thousands were affected in Europe, only 17 children were born with thalidomide-related defects in the U.S.

New legislation following the thalidomide disaster tightened regulations and gave more power to the FDA over drug testing. As the The Washington Post explains, the new regulations forced pharmaceutical companies to conduct phased clinical trials, to be honest about adverse effects and make sure participants give informed consent during drug testing. The law is still in force today.

Kelsey was awarded the Distinguished Federal Civilian Service by President John F. Kennedy. During the White House ceremony, Kennedy, according to The New York Times, said: “Her exceptional judgment in evaluating a new drug for safety for human use has prevented a major tragedy of birth deformities in the United States.”

Just 24 hours before her death, Kelsey was presented with the Order of Canada in a private ceremony. "We knew that death was imminent, and I sat beside her bed, held her hand, told her why I was there and why it was so important that we have the opportunity to recognize her, and took the medal and had an opportunity to put it in her hands," Elizabeth Dowdeswell, lieutenant governor of Ontario, told CBC Canada.