Jan. 4, 2010 -- Using a kitchen spoon to measure liquid medicines, like cough syrup or cold medicine, may make it harder to get the right dosage.

A new study shows that the amount of liquid medicine a person pours into a kitchen spoon depends on the size of the spoon and frequently leads to overdosing or underdosing.

"Participants underdosed by 8.4% when using medium-sized spoons and overdosed by 11.6% when using larger spoons," write researcher Brian Wansink, PhD, of Cornell University, and colleagues in the Annals of Internal Medicine. "Notwithstanding this aggregate bias of 20%, participants had above-average confidence that the doses they poured into both spoons would be equally effective."

The FDA recommends against using kitchen utensils to dose liquid medicines, but researchers say most people still use spoons when pouring medicine for themselves and their families.

In the study, researchers asked 195 university students who were recent patients of the university health clinic during cold and flu season to pour a 5 mL (equivalent to 1 teaspoon) dose of cold medicine into various sizes of kitchen spoons.

To show them what a 5 mL dose looked like, they first gave them a full bottle of cold medicine and asked them to pour a 5 mL dose into a 5 mL teaspoon.

The participants were then asked to pour the same 5 mL dose into a medium-sized tablespoon and a larger spoon. After each pour, the participants indicated how confident they felt that they had poured the proper 5 mL dose.

The study showed the amount of cold medicine that the participants poured varied directly with the size of the spoon. They overdosed by 11.6% when using the larger spoon and underdosed by 8.4% when using the medium-sized spoon, even though they were confident that their pouring was accurate in each case.

Researchers say the consequences of a single 8% to 12% dosing error in a teaspoon-sized serving of medicine may be minimal. But these types of overdosing and underdosing errors are likely to accumulate among tired and sick people who are dosing themselves every four to eight hours for several days.

They say the results suggest that it is safer and much more effective to use a measuring cap, dosing spoon, measuring dropper, or dosing syringe to dispense liquid medicine than to assume the amount poured into a kitchen spoon is accurate.