The birth control shot Depo Provera may impair a person’s memory, according to a new study’s findings, which could have implications for many women.

Depo Provera is a drug approved for use in the U.S. since 1992 requiring an injection every 12 weeks and is 99 percent effective as a birth control alternative.

The study by researchers at Arizona State University connects the hormone active in Depo Provera – medroxyprogesterone acetate – to impaired memory in rodents.

It was published in the journal Psychopharmacology.

The study lasted one year, using three groups of rats which received doses at varying ages and a control group that did not receive hormone.

Rats were placed in water-based mazes to swin and seek out hidden platforms in water.

"What we found was pretty shocking – animals that had been given the drug at any point in their life were memory impaired at middle age compared to animals that never had the drug," said Blair Braden, an ASU psychology doctoral student who led the study together with Heather Bimonte-Nelson, an ASU associate professor of psychology who heads the Bimonte-Nelson Memory and Aging Lab.

"We also confirmed that in the subjects that only received the drug when young, the hormone was no longer circulating during memory testing when older, showing it had cleared from the system yet still had effects on brain function."

The researchers plan to follow the animal studies with human trials.