Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

The Food and Drug Administration approved a device on Tuesday meant to treat cluster headaches — a rare form of headache that affects mostly men.

The gammaCore, a vagus nerve stimulator. GammaCore

The device is a vagus nerve stimulator and it’s not entirely clear how it works. The idea is to disrupt signals that run along the vagus nerve, a giant nerve that runs from the brain all the way to the colon. It's involved in many bodily responses.

A study in the journal Headache last September showed the treatment appeared to help just over a quarter of cluster headache patients who tried it, versus about 15 percent of those given a sham treatment. This went up to about a third of patients with so-called episodic cluster headaches.

A company called electroCore makes the device, called gammaCore.

“GammaCore transmits a mild electrical stimulation to the vagus nerve through the skin, resulting in a reduction of pain,” the company said in a statement.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Cluster headaches are rare but devastating to their sufferers. Like migraines, they cause intense pain and an inability to function much at all when they strike.

Related: FDA Approves New Appetite Pacemaker Device

"Cluster headache is a rare, debilitating and difficult to treat disorder with few effective acute therapies," Dr. Stephen Silberstein, director of the headache center at Jefferson University in Philadelphia, said in a statement.

Fewer than 1 percent of people have cluster headaches and most have a form called episodic cluster headaches, which come and go, as the name suggests, in clusters. Sufferers can go months without an attack and then suffer several sudden headaches in a single day for days on end.

There aren’t many specific treatments but they include the migraine drug sumatriptan, delivered via auto-injector, and inhaled oxygen. Both approaches are limited — it’s not safe to use the injection more than twice a day — and inconvenient.

Related: New Migraine Drugs Would Treat Pain Before it Starts

Silberstein helped test the device, which users press against the neck.

"The FDA release of gammaCore is an important advance in the treatment of the pain associated with cluster headache,” Silberstein said in the statement provided by the company.

“It is a way for patients to treat their symptoms as often as they need to use the device. It does not have the side effects or dose limitations of commonly prescribed treatments or the need for invasive implantation procedures, which can be inconvenient, costly and high-risk."

The company, which says gammaCore is already available in the European Union, expects to start selling it later this year in the U.S.

Vagus nerve stimulation is used to treat a range if disorders, including epilepsy, depression and overeating.

Usually devices are implanted. GammaCore is hand-held.