By Jacqueline Howard, CNN

(CNN) -- Migraine sufferers across the United States have their eyes on a newly approved drug that's offering hope for reducing the frequency of monthly migraine attacks.

On Thursday, the US Food and Drug Administration approved Aimovig for the preventive treatment of migraines in adults with episodic or chronic migraines. Episodic migraine is when symptoms occur zero to 14 days each month; symptoms of chronic migraine occur 15 days or more a month.

Aimovig is the first FDA-approved preventive migraine treatment in a new class of drugs that work by blocking the activity of calcitonin gene-related peptide, or CGRP, a molecule that is involved in migraine attacks. Aimovig targets that molecule's receptor in your body.

The treatment, administered through monthly self-injections, requires a prescription and could be available to patients within a week. Aimovig is expected to cost $575 monthly or $6,900 annually in the United States.

There are three other migraine treatments in this newly emerging class of drugs.

Those drugs target the CGRP molecule itself, instead of its receptor. They are experimental but, if approved, might be made available to patients as early as this fall for one and next year for the others, said Dr. Stewart Tepper, director of the Dartmouth Headache Center at Dartmouth-Hitchcock Medical Center in New Hampshire, who was a clinical investigator in the Aimovig trials.

"When CGRP is released, outside of the brain, it causes inflammation and blood vessel dilation -- the blood vessels get big -- and that combination of inflammation and blood vessels getting big is the pain of migraine," said Tepper, who is also a professor of neurology at the Geisel School of Medicine at Dartmouth College.

Migraine is three times more common in women than in men and affects more than 10% of people worldwide, the FDA noted. In the US, about 12% of the population gets migraine headaches.

What was found in clinical trials

The effectiveness of Aimovig was evaluated in three key clinical trials.

The first included 955 people with a history of episodic migraine. Over the course of six months, those who received the treatment experienced one or two fewer monthly migraine days, on average, compared with a placebo.

The second study included 577 patients with a history of episodic migraine. Over the course of three months, those who received Aimovig treatment experienced one fewer migraine day per month.

The third study evaluated 667 patients with a history of chronic migraine. Over the course of three months, patients treated with Aimovig experienced, on average, 2½ fewer monthly migraine days than those receiving a placebo.

"It may not get rid of all of them, but it really dramatically improves the frequency, severity and duration of the migraine attacks," Tepper said of the new treatment.

Patients "still will need to take something when they get a migraine attack, but this is the first designer medication to prevent migraine rather than treat as needed," he said.

In the clinical studies, the most common adverse side effects were pain at the injection site and constipation. The drug can be injected in the thigh, the abdomen or the outer area of the upper arm.

"The field is excited about a new drug that is specifically targeted for migraine mechanisms," said Dr. Teshamae Monteith, assistant professor of clinical neurology at the University of Miami and a member of the American Academy of Neurology, who was not involved in the development of the drug.

"Not only does the data show that it's effective for people who have what we call episodic migraine, but it's also effective for people who have chronic migraine," Monteith said.

"If you can imagine, a patient with chronic migraine has at least 15 days -- half the month -- with some type of headache, and eight days out of that month, it's what you would call a moderate to severe headache with associated symptoms, such as light sensitivity, sound sensitivity, some cognitive dysfunction, [gastrointestinal] symptoms and sometimes visual and motor symptoms," she said. "Patients can have fatigue, concentration impairment, neck stiffness and sometimes mood changes as well."

By Friday, Monteith was already receiving requests for prescriptions and questions about Aimovig from her patients, including Helene Good, who uses injections of Botox to treat her migraines.

'It's really exciting'

"I first heard about it when it showed up on my phone this morning as an article in my news, and I just happened to be on my way to see Dr. Monteith for my treatment today," Good said Friday.

"I read it to my spouse on the way over, and it's really exciting," said Good, a 63-year-old Miami resident who has had migraines since she was in her late teens.

"It's not like just having a bad headache. For me, it manifests in other ways," she said. "One side of my face droops, which sort of looks like I've had a mini stroke. I'm a pretty fast speaker, but my speech gets very slow."

When it comes to migraine treatment options, "you're always hoping and looking for hope," she said.

Treatment options for migraine sufferers typically depend on the frequency and severity of the migraine attacks. Patients who have episodic migraine usually rely on pain medications to treat the migraine pain. To avoid episodes, some patients may stay away from triggers, such as certain foods, lack of sleep or stress.

Before Aimovig, "the FDA-approved preventive medications for episodic migraine were only four. Two of them are beta blockers, anti-blood pressure medicines, and two of them are anti-epilepsy drugs," Tepper said.

"There was one FDA-approved treatment for chronic migraine, which was Botox," he said. For patients, "with our current preventive medicines, they have to take oral medicine every day, with the exception of Botox, which is given in 31 injections every 12 weeks."

Yet a problem with many of those other treatment options is that some are traditionally used for other disorders and have side effects, Monteith said.

"Not only are some of the drugs not effective for every patient, but then there's this issue with tolerability," she said. "Some of these drugs are not well-tolerated. In the right person, it's great, but certainly we need some other option."

Additionally, there are medical devices such as a FDA-approved nerve-stimulating "tiara" called Cefaly, another nerve-stimulating device called gammaCore and even an approach called transcranial magnetic stimulation. Some patients have turned to acupuncture for migraine therapy.

"As a headache specialist, there are a number of treatments that are available for our patients preventively for migraine, but many of them are associated with a lot of different side effects, and we've been waiting for the day when we can have a medication that specifically targets migraine and prevents it in this unique modality and is associated with few side effects," said Dr. Thomas Berk, headache neurologist at NYU Langone Health, who was not involved in the development of the new treatment.

"I've had a number of requests already from patients asking, is it possible to get it to them quickly? What are the ways of getting it, and the big question being, is my insurance going to cover it, which is a question that we don't really know particularly yet," he said. "Everyone's excited about it."