In December 2005, Alex [not his real name], a Montgomery County resident, said he considered taking his own life. The successful, middle-aged professional had been feeling anxious, fearful, agitated and confused.

He was alternately sweating, then shivering uncontrollably. His symptoms continued to worsen; for about a week, he was unable to work and -- of greater concern -- to sleep.

"I still remember lying awake for hours, shaking, all the time feeling as if electric shocks were passing through my body," he said. "The most frightening thing was the overwhelming sense of terror I felt ... I couldn't stop thinking about ways to kill myself."

A psychiatrist confirmed the source of the problem: Alex, who had been prescribed the antidepressant Prozac 16 years earlier to treat mild depression, had decided that he'd been on the medication too long and had cut his daily 40 mg dosage in half. The troubling array of symptoms stemmed from Alex's decreasing his Prozac intake.

Alex required additional medication on a short-term basis to help him return to a normal sleep pattern, and his symptoms subsided over the next few weeks, when he returned to his original Prozac dose.

Prozac, whose generic name is fluoxetine, came on the market in 1986 and is one of a family of drugs known as selective serotonin reuptake inhibitors (SSRIs). This group, which also includes Zoloft, Paxil and Luvox, works by artificially boosting the level of serotonin, a neurotransmitter chemical, in the brain. The drugs are primarily used to treat depression, obsessive-compulsive disorder and panic attacks, but they've also been prescribed to relieve symptoms of premenstrual dysphoric disorder.