The study, published in the Journal of Biological Chemistry, suggests the drug clioquinol reverses the progression of Alzheimer's, Parkinson's and Huntington's diseases in animals -- perhaps because clioquinol acts directly on a protein called CLK-1, informally called "clock-1."

"Clioquinol is a very powerful inhibitor of clock-1," study leader Sigfried Hekimi of McGill University in Montreal said in a statement. "Because clock-1 affects longevity in invertebrates and mice, and because we're talking about three age-dependent neurodegenerative diseases, we hypothesize that clioquinol affects them by slowing down the rate of aging."

The exact age-slowing mechanism is still unknown, but Hekimi said "one possibility is that clioquinol is a metal chelator." Chelation binds ions and is used to treat heavy metals poisoning.

Hekimi said he is optimistic but warns "clioquinol can be a very toxic substance if abused, and far more research is required."

Prescribed for gastrointestinal problems like diarrhea and shigella since 1930, clioquinal was withdrawn from the market after being blamed for an outbreak of subacute myelo-optic neuropathy in Japan in the 1960s. Because scientific studies were not conducted at the time, some researchers think its connection to subacute myelo-optic neuropathy has yet to be proven, the researchers say.