The dangers of mixing medicines

CHOICE investigates adverse events associated with medication and what can be done to prevent them.
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03.Over and under medicating

Unnecessary medicines

Sometimes doctors may feel it’s not their responsibility to withdraw medications prescribed by another doctor, so patients may be prescribed something for a temporary condition that has since resolved. A CHOICE member alerted us to another problem resulting from lack of clear communication between doctor and patient: that of when to stop taking medications with repeat prescriptions. This has also led to patients being prescribed a new brand of a particular medicine — or given a generic instead of a brand – but taking both the old and the new.

A review of 31 studies looking at withdrawing certain medications from older patients found that in many cases, antihypertensives, benzodiazepines and antipsychotics could be successfully reduced or eliminated with no adverse effects, and sometimes lead to improvement in quality of life. In another study, GPs were trained to review medications of elderly people, and following that training were able to successfully reduce the number of medications taken by their patients.

Taking medicines incorrectly

Lack of information, instructions that are difficult to understand and complex regimens can lead to patients not taking medicines correctly. Consumer Medicine Information (CMI) leaflets are available from pharmacists, doctors and the National Prescribing Service for all prescription medicines (they’re sometimes found in the medicine’s packaging), but are not always offered or asked for.

Nor do prescribers always get it right. Australian researchers found that 10% of adults with chronic illness were given the wrong medicine or dose in the previous year. Other research has found about 20% of prescriptions among the general community were of the incorrect dose.


So far, the problems discussed refer largely to over-medication, where too much, too many or the wrong kinds of medicines are taken. Another significant issue is under-medication. There are several reasons for people not taking medicines, including confusion and forgetfulness, or neglect on the part of their carer. Medical professionals may have prescribed too low a dose, or have missed a condition. Patients who suffer side effects may also stop taking medicines, as, conversely, do patients who “feel better”.

It’s estimated about one in five adults with chronic illness skips a dose or doesn’t fill a prescription due to cost. Many older people, and others who require lots of medicine, have a concessionary status that entitles them to low-cost medicines. They pay a nominal amount for prescriptions, called a co-payment, and when they (or their family) have spent a certain amount — up to the safety net threshold – in a one-year period, prescriptions are free for the rest of that year.

Even a small increase in the co-payment amount can reduce medicine taking. In 2005, an increase from $3.70 to $4.60 had a noticeable effect on the number of prescriptions being filled, with low-income members of the community choosing to forgo certain medicines. Subsequent research on this found the greatest drop was for medicines prescribed for chronic but asymptomatic conditions, such as:

  • anti-platelet medicine (to prevent blood clots)
  • osteoporosis treatments
  • combination (prevention and symptom control) asthma medicines and proton-pump inhibitors (used to treat gastro-oesophageal reflux)

While some of these can be replaced by over-the-counter medicines, there’s no way of knowing to what extent this occurred.


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