Sweating off high anxiety
CU study shows exercise reduces anxiety caused by Prozac
By Clint Talbott
Prozac can ease depression and anxiety, but high doses can backfire, at least initially. In humans and rats, acute doses of fluoxetine, the generic form of Prozac, can increase anxiety. This is problematic because this initial increase in anxiety can cause people to either quit taking the antidepressant or acutely increase their risk of suicide.
Regular exercise may ward off or at least diminish the anxiety caused by acute doses of the antidepressant. That’s the novel conclusion of a study published last year by a team of University of Colorado researchers in the journal Psychopharmacology.
Benjamin N. Greenwood, a post-doctoral fellow in the laboratory of Associate Professor Monika Fleshner at CU’s Department of Integrative Physiology, led the study. His team included graduate students Paul V. Strong and Leah Brooks.
The team studied differences between sedentary rats and rats that had been voluntarily running in wheels for at least six weeks. Among the sedentary and active rats, some were given “acute” doses of fluoxetine and others were given saline as a control.
Acute doses of Prozac, compared to saline control, produced dose-dependent increases in anxiety-like behavior in sedentary rats. This increase in anxiety is similar to that found in some people during initial treatment with antidepressants.
Six weeks of wheel running “significantly reduced the acute behavioral effects of fluoxetine,” the study says.
Greenwood says regular exercise seems to alter the ability of Prozac and other selective serotonin reuptake inhibitors (or SSRIs) to produce anxiety, but that exercise does not alter every effect of SSRIs.
“This suggests that exercise does not prevent SSRI-induced anxiety by altering the metabolism of the SSRI, or some other non-specific effect,” Greenwood says. “Instead, exercise may alter the expression or function of a target in the brain where the SSRI acts to produce anxiety-like behaviors.”
While exercise is known to reduce anxiety in humans, Greenwood says there is no study of which he’s aware that has investigated whether regular exercise can affect a person’s initial anxiety response to an antidepressant.
“This would be an important study given the results we found in the animal model.”
That’s partly because humans sometimes stop taking antidepressants if they feel more anxious. Greenwood’s study suggests that regularly exercising humans might feel less anxious and be more likely to continue taking the drugs.
He adds: “This is a good thing because over the long run—once the initial increase in anxiety is out of the way—continuation of SSRI therapy can help reduce depressive symptoms.”
The results of this experiment suggest that a history of physical activity might predict individuals’ initial anxiety response during the onset of treatment with SSRIs, Greenwood says. “This does not imply that sedentary individuals should stay clear of SSRI therapy.”