Nov 26 (Reuters) - The U.S. Food and Drug Administration rejected Avanir Pharmaceuticals Inc's migraine drug device, a few weeks after the regulator had raised questions regarding some data submitted as part of the marketing application.

Earlier this month the FDA had asked Avanir to assess the root cause of errors observed in the data from the drugmaker's human factors study, which assesses if patients can use a device safely and effectively.

The product, AVP-825, delivers a low-dose sumatriptan powder - the most commonly prescribed migraine medicine - through the nose.

Avanir on Wednesday said it would conduct a new human factors study and respond to the FDA's complete response letter in the first half of next year.

The FDA was slated to decide on the product on Nov. 26.

Analysts remained confident of the product's eventual approval as the FDA only raised concerns related to the device rather than the product's active ingredient.

Cowen & Co analysts have said they expect the delay to push the launch of the drug to early 2016.

Over 37 million Americans suffer from migraines, according to the Centers for Disease Control and Prevention.

Avanir's sole treatment on the market, Nuedexta, is a treatment for pseudobulbar affect, a disorder characterized by laughing or crying that often accompanies underlying neurological disease.

The drug is also being developed for use in a host of other diseases, including Alzheimer's-related agitation as well as Parkinson's and depression.

The Aliso Viejo, California-based company's shares closed up 4 percent at a eight-year high of $15.01 on Wednesday.

The stock had risen about 14 percent since Nov. 7 when the company said the migraine drug device's approval was unlikely this year.

(Reporting by Natalie Grover in Bangalore; Editing by Savio D'Souza)