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Like Kleenex and Band-Aid, Botox is a brand name that's become indistinguishable from the product. But in a new randomized study, Botox's newer competitor, Dysport, appeared to have the edge in smoothing wrinkles.

Botox (onabotulinumtoxinA) was approved by the Food and Drug Administration (FDA) to treat frown lines — those pesky wrinkles between the eyebrows — in 2002. In 2009, a competitor, Dysport (abobotulinumtoxinA) was approved for the same use.

Both drugs have also been approved for other cosmetic and medical uses, and doctors administer them widely to smooth wrinkles even in areas they haven't been specifically approved to treat, namely around the outer corner of the eyes.

The new study aimed to figure out which product worked better to improve the appearance of such creases, known as crow's feet — the wrinkles that fan out when you smile, laugh or squint. Researchers from the Maas Clinic in San Francisco and University of California, San Francisco, enrolled 90 people for a "split face" study in which doctors randomly injected Botox into one side of the face and Dysport into the other.

Using a five-point scale, the researchers then evaluated results on both sides of the participants' faces; the patients themselves were also asked to indicate which side they preferred. According to the researchers' measure, Dysport improved the appearance of crow's feet significantly better than Botox did. At the 30-day mark, about two-thirds of participants said they also favored the side that had been treated with Dysport. But the difference was seen only when users contracted their facial muscles as much as possible. There was no difference in appearance when faces were at rest.

The authors, who published their findings Monday in the Archives of Facial Plastic Surgery, said that additional research would be necessary to determine whether Dysport would prove more effective in other areas of the face and why the two drugs might work differently.

A caveat: the makers of both Botox and Dysport — Allergan Inc. and Medicis Aesthetics, respectively — were asked to help fund the study, but only Medicis paid for the research.

• Meredith Melnick