Around 20 per cent of older patients are taking multiple drugs that are cancelling each other out, and could be making a condition worse.
The best approach may be to treat only the more serious conditions and prescribe one drug at a time, say researchers at Oregon State University.
Although some doctors are aware of the serious adverse reactions that can result from 'polypharmacy'-prescribing more than one drug at the same time-they don't have the skill or knowledge to change their approach, the researchers say.
In a study of 5,815 adults, the researchers discovered that 22 per cent of them were taking a prescription drug that could worsen another health problem they had. One typical example was patients who have heart disease and chronic obstructive pulmonary disease (COPD); beta blockers are commonly prescribed for heart problems, but the drugs worsen COPD.
Other chronic health problems that are made worse by polypharmacy include hypertension (high blood pressure) and osteoarthritis; hypertension and diabetes; hypertension and COPD; diabetes and coronary heart disease; and hypertension and depression.
Overall, the researchers say, around 9 million Americans alone could be prescribed drugs that are doing more harm than good.
Aside from making a condition worse, taking multiple drugs can also lead to falls, delirium, dizziness, fatigue and anorexia.
(Source: PLoS ONE, 2014; 9 (2): e89447)