SUNDAY, Feb. 20 (HealthDay News) -- Taking prescription amphetamines may raise your risk of developing Parkinson's disease later, new research suggests.

But, the researchers noted that the study did not prove a cause-and-effect relationship and further investigation is warranted.

Study author Stephen K. Van Den Eeden, a senior investigator at the Division of Research at Kaiser Permanente Northern California, in Oakland, said that people who reported using Benzedrine or Dexedrine at some point in their lives showed a 60 percent greater chance of developing the neurological disorder when compared to those who said they had never taken the medications.

"We already know that there are certain risks of amphetamine use," Van Den Eeden said. "This is one concern that is unproven, but we need to take into consideration whether the benefits outweigh the known risks, and maybe potential risks."

Amphetamines affect the release and absorption of dopamine, a key neurotransmitter implicated in the development of Parkinson's disease, according to background information in the report. They are commonly prescribed for the treatment of attention-deficit hyperactivity disorder (ADHD), traumatic brain injuries and a chronic sleep disorder known as narcolepsy. These medications were also being routinely prescribed for weight loss when the research first began.

Between 1964 and 1973, 66,348 study participants answered two questions concerning amphetamines: The first asked if the person had ever taken weight-loss drugs in general, while the second asked about the use of Benzedrine and Dexedrine in particular. After 1995, researchers followed up on the participants and found that 1,154 had been diagnosed with Parkinson's. The mean follow-up period was 38.8 years. While those who said they had taken Benzedrine or Dexedrine showed an increased risk for being diagnosed with Parkinson's, those who simply said they had taken weight-loss drugs in general did not.

Dr. Stacy Horn, an assistant professor of clinical neurology at the University of Pennsylvania's Parkinson's Disease & Movement Disorders Center in Philadelphia, explained that patients and doctors considering prescription amphetamine use should consider the risk-vs.-benefit ratio.

"Someone who failed all the other classic medicines might consider drugs such as amphetamines," said Horn, who added that further research on the possible connection to Parkinson's is needed.

"We need to confirm the science," said Horn. "There needs to be some increased surveillance. We should look at patients that have had an addiction, and see if there's an increased risk in those populations."

Horn also emphasized that researchers still don't understand what factors might explain the development of Parkinson's disease, although previous research has hinted at a link to exposure to environmental toxins.

"Part of the problem," Horn explained, "is not knowing if this is a direct correlate or exposure to something else."

The research was released Feb. 19, and is scheduled to be presented in April at the American Academy of Neurology's annual meeting in Honolulu.

Since this study is slated to be presented at a medical meeting, the data and conclusions should be considered preliminary until published in a peer-reviewed journal.

More information

Find out more about Parkinson's disease at the U.S. National Institute of Neurological Disorders and Stroke.