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A new study has linked Ecstasy use to memory loss, researchers in Germany have found.

Dr. Daniel Wagner said he tracked more than 100 recreational Ecstasy, or MDMA, users over the course of a year and found that they didn't perform as well on a series of tests at the end of the study. He said the damage was most evident in associative memory. For example, Ecstasy users might have difficulty remembering where they put their keys.

"Given the relatively small amounts of MDMA that were used, and given the relatively short time period of one year, we were quite surprised at these specific effects," Wagner told ABCNews.com.

Those Ecstasy users took an average of 32 pills over the year, or slightly more than one pill every other weekend. Dr. Stephen Ross, director of Addiction Psychiatry at New York University's Tisch Hospital, said the findings weren't new or surprising. Other researchers had similar results in 2007.

"It is a drug that certainly can be problematic," Ross said.

He also said Wagner's findings should also be taken with a grain of salt, because Wagner and his team didn't use any brain imaging to confirm damage to the hippocampus, the part of the brain that plays an important role in long-term memory.

He said it's also not clear whether cannabis - which was not controlled for in the study - played a role in the memory loss he saw in his patients. Studies find cannabis can cause memory impairment.

"The study doesn't necessarily rule out the fact that other things caused this," Ross said.