What's more, at least 40 million Americans suffer chronic or repeated headaches, and some 10 million people visit physicians for headaches annually.

Such statistics, from national headache organizations, do little to convey the excruciating pain of many headaches.

And for all the advances in treatment and rapid growth in the array of prescription and over-the-counter drugs, many people still suffer needlessly from headaches, experts say.

That's a problem health officials hope to overcome during National Headache Awareness Week, which concludes today.

"They're under-diagnosed, under-treated and misunderstood," says Dr. Seymour Diamond, executive chairman of the National Headache Foundation.

He says managed care is partly to blame, often resulting in a rushed doctor visit and a prescription. "To take care of a headache patient, you've got to sit down about an hour and talk to them," Diamond says. "It's not just prescribing a drug."

Primary-care doctors often don't spend the time necessary to assess the headache patient thoroughly and decide on the best course of treatment, says Diamond, director of the Diamond Headache Clinic in Chicago. Physicians should do a complete physical exam and assess the pain, its frequency and location, other symptoms and possible contributing factors, he says.

Overuse of both prescription and over-the-counter pain relievers can make matters worse by causing "rebound" headaches, Diamond says.

Headache sufferers also often resign themselves to suffering pain they view as inevitable, says Dr. Ellen Drexler, associate attending neurologist and director of the headache unit at Maimonides Medical Center in New York City.

"People sort of accept [headaches] as almost part of the human condition," she says. As a result, she says, "A lot of people with headaches never do get diagnosed and don't get proper attention."

To determine the best treatment, the doctor must first diagnose the type of headache, experts say.

More than 90 percent of headaches are so-called primary headaches -- those in which the headache is not the symptom of another medical condition, says the American Council for Headache Education.

Headaches can be triggered by numerous causes, including certain foods, odors, changes in the weather, menstrual periods, stress, depression, anxiety and frustration. The council also points to medical evidence suggesting that primary headaches could be caused by electrical and chemical instability in brain centers that regulate blood vessels and pain messages into the brain.

Primary headaches include tension, migraine and cluster headaches.

Tension headaches:

Tension headaches are the most common type, affecting as many as 90 percent of adults at some point, the council says. These headaches are characterized by a steady ache on both sides of the head, and they can be chronic.

But "tension headache" often is something of a catch-all term, Drexler says. "When we don't know what to call a headache, we often call it a tension headache," she says. "We understand a lot less about the cause of tension headaches than migraines. We definitely have a long way to go in terms of understanding tension headaches."

Some tension headaches can be treated with such over-the-counter remedies as aspirin, ibuprofen and acetaminophen. Persistent tension headaches often respond to some antidepressants, including those regulating the neurotransmitter serotonin, as well as anti-inflammatory medicines and muscle relaxants, the National Headache Foundation says. The foundation says other treatments, such as relaxation training, biofeedback and massage sometimes help relieve tension and migraine headaches.

Migraines:

About 30 million Americans, three-quarters of them women, suffer migraines, and up to half of all migraines are never diagnosed, experts say.

Migraines produce intense, throbbing pain, typically on one side of the head, in addition to nausea and sensitivity to light and sound.

A better understanding of migraines and medical breakthroughs have improved treatment significantly. Triptans, which can stop migraine pain, hit the market in 1993. Beta blockers and calcium channel blockers, both used to treat high blood pressure and coronary artery disease, help reduce the frequency and severity of migraines, and antidepressants that affect serotonin levels have helped migraine sufferers.

Some anti-seizure medications used to treat epilepsy and bipolar disorders also appear to prevent migraines, while wrinkle-removing Botox appears to help prevent migraines or reduce their frequency and severity, researchers say.

New treatments notwithstanding, many migraine sufferers take too many addictive medications that give only short-term relief, instead of using newer, more effective drugs, Wake Forest University School of Medicine researchers reported in a recent study.

And migraine patients, the study added, often don't get the best treatments for the debilitating ailment because they see primary-care physicians, not specialists who are much more likely to prescribe the newer medications, such as triptans.

Cluster headaches:

Cluster headaches affect about 1 percent of the U.S. population, says the headache council. Unlike migraines, cluster headaches strike more men than women, and the severe pain that they cause normally lasts no more than an hour or two. These headaches always occur on the same side of the head, often around one eye, which may become inflamed or redden.

As the name implies, cluster headaches usually occur in clusters that can last four to eight weeks and may strike every few months, the American Academy of Family Physicians says.

Preventive drugs as well as those that relieve headaches, including triptans, can be used to treat cluster headaches, the headache foundation says.

Some headaches could be a sign of a serious medical condition. The headache council recommends you contract your doctor if:

• Your headache is accompanied by a stiff neck, fever, shortness of breath, dizziness, drowsiness, severe vomiting, unsteadiness, weakness, slurred speech, numbness, tingling, or unexpected symptoms affecting your eyes, ears, nose or throat.
• You have three or more headaches a week.
• You take a pain reliever daily or almost daily.
• You take more than recommended doses of over-the-counter medications.
• Your headaches are triggered by exertion, coughing, bending or sex.
• Your headache keeps worsening and won't go away.
• Your headaches began after age 50.
• Your headaches began after a head injury.

More information

For more on headaches, their causes and treatments, visit the National Headache Foundation or the American Council for Headache Education.