Here’s a warning for Hillary Clinton, Bernie Sanders and Donald Trump. Before getting government more involved in controlling drug prices, take a close look at the mistakes that have already been made (and that are not being corrected) and the human suffering these mistakes are causing.

In hospitals, clinics and doctors’ offices around the country medical doctors are dealing with a problem that you might expect to find only in an undeveloped country: a shortage of drugs, often life-saving drugs. I first wrote about this problem in Health Affairs five years ago. Since then, the problem has only grown worse, as the chart below shows.

These drugs are often generic drugs and they are usually not very expensive. Cancer drugs, for example, are typically injected by a doctor, who purchases them and then re-bills Medicare. But because of Medicare’s price controls, when shortages occur they are not eased by market clearing prices, as they would in other markets. As a result, providers sometimes turn to more expensive and often less appropriate brand drugs. More often than not, patients are simply denied the treatments they need.