The Food and Drug Administration has approved a controversial new drug for the fatal condition known as ALS, or Lou Gehrig's disease.

The decision is being hailed by patients and their advocates, but questioned by some scientists.

Relyvrio, made by Amylyx Pharmaceuticals of Cambridge, Mass., was approved based on a single study of just 137 patients. Results suggested the drug might extend patients' lives by five to six months, or more.

"Six months can be someone attending their daughter's graduation, a wedding, the birth of a child," says Calaneet Balas, president and CEO of the ALS Association. "These are really big, monumental things that many people want to make sure that they're around to see and be a part of."

Balas says approval was the right decision because patients with ALS typically die within two to five years of a diagnosis, and "right now there just aren't a lot of drugs available."

But Dr. David Rind, chief medical officer for the Institute for Clinical and Economic Review, isn't so sure about Relyvrio, which will cost about $158,000 a year.

"I totally understand why people would be trying to figure out a way to get this to patients," he says. "There's just a general concern out there that maybe the trial is wrong."

ALS kills about 6,000 people a year in the U.S. by gradually destroying nerve cells that control voluntary movements, like walking, talking, eating, and even breathing. Relyvrio, a combination of two existing products, is intended to slow down the disease process.

Proponents of the drug say the small trial showed that it works. But FDA scientists and an expert panel that advises the FDA, weren't so sure.

Typically, FDA approval requires two independent studies – each with hundreds of participants – showing effectiveness, or one large study with clearly positive results.

In March, the Peripheral and Central Nervous System Drugs Advisory committee concluded that the Amylyx study did not provide "substantial evidence" that its drug was effective. Then in September, during a rare second meeting to consider a drug, the panel reversed course and voted in favor of approval.

The second vote came after Dr. Billy Dunn, director of the FDA's Office of Neuroscience, encouraged the committee to exercise "flexibility" when considering a drug that might help people facing certain death.

A much larger study of Relyvrio, the Phoenix Trial, is under way. But results are more than a year off.

A negative result from that study would be a major blow to Amylyx and ALS patients.

"If you've got a drug that's extending life by five months," Rind says, "you ought to be able to show that in a larger trial."

In the meantime, he says, perhaps Amylix should charge less for their drug.

Relyvrio (marketed as Albrioza in Canada) is the only product made by Amylyx, a company founded less than a decade ago by Joshua Cohen and Justin Klee, who attended Brown University together.

Klee defends the drug's price, saying it will allow the company to develop even better treatments. "This is not a cure," he says. "We need to keep investing until we cure ALS."

Klee and Cohen have also promised that Amylyx will re-evaluate its drug based on the results of the Phoenix trial.

"If the Phoenix trial is not successful," Klee says, "we will do what's right for patients, which includes taking the drug voluntarily off the market."

But that the decision would require support from the company's investors, and its board of directors.