Researchers from Ghent University in Belgium told there could be "serious clinical consequences" for patients.
Tablets which have a slight margin between a dose that is therapeutic and one that is toxic are riskiest.
The study was published in the Journal of Advanced Nursing.
Researchers from Ghent University asked five volunteers to split eight different sized tablets using three different methods.
The participants used three different methods to split the pills a expert splitting device, scissors and a kitchen knife. The pills were various shapes and sizes.
