A Washington doctor warned that he has seen three children complain of headaches caused by the physical stress of relentlessly plowing through the epic 870-page adventure.

Call them Hogwarts headaches, named after the wizard school that Harry attends.

Dr. Howard Bennett of George Washington University Medical Centre wrote in a letter to this week's New England Journal of Medicine that the three children, ages 8 to 10, experienced a dull headache for two or three days.

Each had spent many hours reading "Harry Potter and the Order of the Phoenix."

After ruling out other potential causes, Bennett told his patients to give their eyes a rest. But the spell cast by the book was clearly too powerful.

"The obvious cure for this malady -- that is, taking a break from reading -- was rejected by two of the patients," Bennett said, adding that the children took acetaminophen instead.

In each case, the headache went away only after the patient turned the final page.

"Order of the Phoenix," the fifth book in the series, has nearly three times as many pages as "Harry Potter and the Sorcerer's Stone," the first book, and Rowling still plans two more tomes.

"If this escalation continues as Rowling concludes the saga, there may be an epidemic of Hogwarts headaches in the years to come," Bennett predicted.

(Agencies)