ow that the Food and Drug Administration has warned Americans taking antidepressants to be on the lookout for potentially harmful side effects, including severe restlessness and suicidal thinking, some people may end up stopping the drugs. But going off antidepressants can bring its own problems.
Stopping cold turkey can cause an array of troublesome symptoms, the most common being dizziness, which can last for days on end. Flu-like feelings, including nausea, headache and fatigue, are also common, as are intense feelings of anxiety, irritability or sadness. Some patients experience alarming sensations of tingling or burning in various parts of the body; ringing in the ears; blurred vision; or flashing lights before the eyes. Some people even describe a feeling of shock waves pulsing through their arms and legs, as if they had been zapped with a jolt of electricity, a condition sometimes called lightning-bolt syndrome.
"The feeling can be really abrupt, like a quick jerk of the muscle," said Dr. Richard C. Shelton, a professor of psychiatry at Vanderbilt University. "It's not painful, but it can be very frightening to people."
Internet bulletin boards and Web sites devoted to antidepressant withdrawal chronicle the crying spells, vertigo and nightmares that people sometimes experience.
"I feel like my brain is floating in Jell-O, slamming into the sides of my skull every time I move my head or my eyes," one person wrote.
Another described palpitations, night sweats and "bloody hideous nightmares."
To avoid such symptoms, or at least hold them to a minimum, the drugs need to be tapered gradually in most cases, and that means quitting under a doctor's supervision. Psychiatrists say it is unwise for people who are taking antidepressants simply to quit on their own.
In its warning, issued in March, the F.D.A. urged doctors to closely monitor patients taking antidepressants, especially during the first weeks of therapy or when changing dosage. Signs of trouble, the agency said, could include suicidal thoughts, severe restlessness, anxiety, hostility or insomnia. Though an association between antidepressants and suicidal thinking or behavior has not been proved, unpublished studies suggesting the possibility of such a link in children and adolescents have caused concern. The F.D.A. is still investigating the issue.
The drugs most likely to produce withdrawal symptoms act on the brain chemical serotonin. These drugs work by blocking the action of a protein in the brain that normally transports serotonin out of the synapses, the spaces between brain cells. With the transporter protein blocked, serotonin lingers in the synapses, and that can have a positive effect on mood.
When the drug is taken away, there is suddenly less serotonin in the synapses. Serotonin receptors in the brain, accustomed to a larger supply of the neurotransmitter, may take days or weeks to adjust, said Dr. Ephrain C. Azmitia, a psychopharmacologist at New York University.
"You get a precipitous drop in all the things that serotonin does in the brain, including its effects on appetite, sleep, sensory perception and emotions," Dr. Shelton said.
Not everyone experiences withdrawal symptoms. Studies suggest that only 10 to 20 percent of patients have significant problems, said Dr. Jerrold F. Rosenbaum, chief of psychiatry at Massachusetts General Hospital in Boston. And some patients find the effects less intense or bothersome than others.
Doctors say people who have been taking especially large doses of a drug for many years may be somewhat more vulnerable. Which drug a patient is taking also makes a difference. Some are stronger than others, and some are metabolized by the body more quickly.
The longer a drug's half-life - the time it takes for half the amount of drug in the body to be eliminated - the less likely it is to cause withdrawal problems. Eli Lilly's Prozac, for example, has a long half-life, remaining in the body for days or even weeks after someone stops taking it. As a result, people who take it are less likely to experience withdrawal effects.
"With Prozac, it can take six weeks for any symptoms to occur," Dr. Rosenbaum said, and even then the effects are mild, with about 5 to 6 percent of people experiencing mild dizziness.
GlaxoSmithKline's Paxil, on the other hand, generally leaves the body in a day or two. Effexor, made by Wyeth, disappears faster still.