Some particularly unlucky patients can have side effects that are impossible to live with and then a change is often recommended if available. Others have side effects that they just have to live with if they are to have their illness effectively controlled, as sometimes there is no alternative.
It is not surprising given the severity of some of these side effects that some patients stop taking them, or reduce their dose by taking the drug less often than recommended. Some even stop taking the drug altogether without informing their doctor. This can have severe consequences for the patient. After a short lived boost to their quality of life as the side effects recede the patient then becomes increasingly exposed to the even more severe long term consequences of the illness they were being treated for.
Although there is no doubt that the patients experiences the worst of the consequences of their decision to stop medication there are other broader implications. Failing to take a drug for a chronic condition can lead to earlier and more frequent hospitalisation and earlier nursing home requirements. Putting aside the argument that this means a hospital bed or nursing home placement is needlessly filled (blocking others) there is the question of all the extra expense needed. A recent report suggests that the cost in the US could be as high as $300 billion a year (!!), suggesting that there are extremely significant savings that could be made in the UK NHS too.
How big is this problem? This is perhaps the most shocking statistic of all - of those people given drugs to treat chronic illness in the US 50% don't take their medication as prescribed.
Researchers are working to find ways to identify those patients who are most likely to not take their medication and thus be able to target ways to assist them and reduce this massive problem.