Gary Wadler testifying at a 2005 congressional hearing on the use of steroids in baseball. (Gerald Herbert/Associated Press)

Gary Wadler, who was among the first doctors to draw attention to the dangers of steroids and other performance-enhancing drugs and whose anti-doping efforts led to stricter testing and sanctions at the Olympic Games and in major sports leagues, died Sept. 12 at his home in Port Washington, N.Y. He was 78.

The cause was multiple system atrophy, said his wife, Nancy Riseman Wadler.

A self-described nonathlete with “two left feet,” Dr. Wadler nonetheless became a specialist in sports medicine after being named the official physician of the U.S. Open tennis tournament in 1980.

While working at the tournament in 1986, Dr. Wadler and other officials were asked to provide urine samples for drug testing, which led to his interest in how athletes sought to improve their performance through illicit means.

He and another physician, Brian Hainline, published a 1989 book, “Drugs and the Athlete,” which described various illegal substances used by athletes over the years and the dangers associated with them. (One of the earliest drug-related deaths among athletes came in 1960, when an Olympic cyclist died after using amphetamines.)

Dr. Wadler, whose specialty was internal medicine, examined the effects of steroids, human growth hormone and other performance-enhancing drugs as a professor of medicine at New York University and later at what is now the Zucker School of Medicine at Hofstra/Northwell in New York.

He maintained steroids could cause heart trouble and liver damage, as well as reproductive problems, breast growth in men and severe depression.

He cited examples of young athletes dying from enlarged hearts or of suicide after using steroids.

In addition to the harmful effects of performance-enhancing substances, Dr. Wadler also warned of something almost as pernicious: an undermining of the morality of sports.

“Cheating strikes at the heart of the value system in the sports structure,” he told USA Today in 2003. “Sports is supposed to be a contest of character. When it becomes a contest of chemistry and pharmacology, that’s a tragedy.”

In 2000, Dr. Wadler helped found the World Anti-Doping Agency, which oversees drug testing at the Olympics, and chaired its committee on prohibited substances. He was instrumental in drawing up year-round testing procedures and a stiff set of penalties, currently a four-year ban for athletes who test positive.

Dozens of Olympic medalists have been caught cheating, including U.S. sprinter Marion Jones, who had to relinquish three gold medals and two bronze medals from the 2000 Summer Games after she was revealed to have used banned substances.

In 2005, after baseball had seen a steroid-fueled surge in home-run hitting, Dr. Wadler testified at a congressional hearing about the prevalence of steroids and other drugs in the sport. He criticized baseball’s lax testing standards, which nevertheless turned up a substantial number of players abusing performance-enhancing drugs.

He also lashed out at the National Football League for ignoring what he considered the widespread use of steroids and human growth hormone (HGH). As part of a federal investigation in 2006, Dr. Wadler examined the records of a South Carolina doctor who was later sentenced to prison for prescribing large amounts of performance-enhancing drugs to NFL players.

“When I travel around the world,” Dr. Wadler said in 2007, “the first thing people ask [is] ‘Why do you let players get away with this stuff?’ It’s the player associations. They should be looking out for the real health and welfare of their members, not just financial health. It will be the clean athletes who don’t want this problem to grow who will make the difference.”

Under pressure from the public, Major League Baseball and its powerful players union eventually agreed to harsher penalties, including a 50-game suspension for a positive first test. The NFL began to test for HGH in 2014.

Gary Irwin Wadler was born Jan. 12, 1939, in Brooklyn. His father was a window dresser for stores, his mother a teacher.

After graduating from Brooklyn College, Dr. Wadler received his medical degree in 1964 from Cornell Medical School (now Weill Cornell Medicine) in New York. He had a medical practice in Manhasset, N.Y., where he was chief medical resident at North Shore University Hospital.

As the physician at the U.S. Open in 1991, Dr. Wadler advised Jimmy Connors to give up drinking soft drinks throughout the tournament to prevent cramping.

“There’s caffeine in cola, and caffeine is a diuretic,” Dr. Wadler told Newsday in 2003. “You’re playing five-set matches in the heat, you’re going to have a real problem with dehydration. Without the cola, Connors’s cramping disappeared.”

At the age of 39, Connors had one of the most remarkable performances in U.S. Open history, overcoming younger competitors before finally losing in the semifinals — a tournament Connors later called “the greatest of my life.”

In addition to his anti-doping work, Dr. Wadler was an adviser to the Justice Department and a White House drug control panel. He chaired the medical advisory board of the American Ballet Theatre and edited a book, “The Healthy Dancer.”

Survivors include his wife of 45 years, Nancy Riseman Wadler of Port Washington; two children, David Wadler of New York and Erika Wadler of Los Angeles; a brother; and two grandchildren.

In 2004, Dr. Wadler was the founding chairman of the Taylor Hooton Foundation, which seeks to educate young people about the dangers of performance-enhancing drugs.

It is named for a high school baseball pitcher in Texas who committed suicide after taking steroids.

One of Dr. Wadler’s greatest fears was the public would grow numb to the presence of steroids and would begin to accept them — and their dangers — as a part of the modern sporting landscape.

“If we fail at this, if we let this problem go unchecked,” he said in 2004, “the playing field will no longer be level,” Wadler says. “We cannot allow this kind of behavior to rule the day and become the prevalent culture. People will lose faith in sports.