The prescribing information on antidepressants specifically warns that patients should be monitored for symptoms like anxiety, agitation, panic attacks, mania and akathisia. “There is concern that such symptoms may represent precursors to emerging suicidality,” the labels say, especially if they were “abrupt in onset” or “not part of the patient’s presenting symptoms.”

Akathisia is, by definition, a drug-induced syndrome. The word comes from Greek and means “not to sit,” referring to an inability to sit still. Akathisia is characterized by anxiety, restlessness and a compulsion to move or walk about; patients may pace back and forth, or fidget endlessly in their chairs.

It may develop when a patient, adult or younger, begins treatment, but it can also emerge when the dosage of the drug is increased, decreased or discontinued. Patients who have tolerated a drug in the past may develop akathisia when they start a new course of treatment, experts say.

Akathisia is a fairly common and well-known side effect of antipsychotic medications, commonly used to treat disorders like schizophrenia but increasingly given for a variety of mental health complaints, including depression. But the association with antidepressants is not as well recognized, experts say, and incidence rates are hard to pin down.

A group of psychopharmacologists who reviewed over 100 studies found the reported rate of what they broadly called “jitteriness/anxiety syndrome” — which they defined as a worsening of anxiety, agitation and irritability — ranged from 4 percent to 65 percent among patients initiating treatment with selective serotonin reuptake inhibitors, or S.S.R.I.s, the popular class of antidepressants to which Paxil belongs.

Psychiatrists linked S.S.R.I.-induced akathisia to suicidal behavior in a 1991 paper describing three patients who survived violent suicidal attempts — including jumping off the roofs of buildings and off a cliff — shortly after they had started fluoxetine or had the dose increased.

The patients were removed from the drug, but then agreed to try another course of treatment with fluoxetine under close observation. All three became extremely agitated and had a recurrence of suicidal thoughts.