SEATTLE -- Depression is an illness of the mind and body. It's very common -- affecting more than 18 million Americans.

Depression may occur only once in a person's life. Or it may be a chronic condition, requiring ongoing treatment over a lifetime. Often, however, it occurs repeatedly with depression-free periods in-between.

Thankfully, there are many effective medications to treat depression. And yet...

“As many as 20 or 25 percent of the patients still won’t respond," said Dr. David Mrazek, a Mayo Clinic Psychiatrist.

But Mrazek says there are options for patients with medication-resistant depression.

Psychotherapy, talk therapy and electro-convulsive therapy have been available for many years.

The emerging field of “pharmacogenomics” is another avenue. That's when a patient's genetic makeup is used to determine the best drug. Dr. Mrazek has this message for young patients still struggling with depression.

"It’s important for them to realize that in their lifetime, they may have an opportunity to be helped by a medication that was designed for them," he said.

More information on Depression

Mayo Clinic

National Institutes of Health