Coffee can help tame the tremors caused by Parkinson's disease, research has shown.
Scientists gave 61 patients caffeine pills equivalent to drinking two to four cups of coffee a day, or an inactive "dummy" treatment.
After six weeks, those taking the caffeine averaged a five-point improvement in symptom severity ratings.
"Studies have shown that people who use caffeine are less likely to develop Parkinson's disease, but this is one of the first studies in humans to show that caffeine can help with movement symptoms for people who already have the disease," said lead researcher Dr Ronald Postuma, from McGill University in Montreal, Canada.
"This is a modest improvement, but may be enough to provide benefit to patients."
The caffeine group also averaged a three-point improvement in speed of movement and stiffness compared with non-treated patients.
The findings are reported in the online issue of the medical journal Neurology.
Dr Michael Schwarzschild, from Massachusetts General Hospital in Boston, US, who wrote an editorial accompanying the research, said: "The study is especially interesting since caffeine seems to block a malfunctioning brain signal in Parkinson's disease and is so safe and inexpensive.
"Although the results do not suggest that caffeine should be used as a treatment in Parkinson's disease, they can be taken into consideration when people with Parkinson's are discussing their caffeine use with their neurologist."
The authors point out that the study was short and the effects of caffeine may lessen over time.