In all industries, monopolies and oligopolies limit choice and extract economic rent. In medicine, they do so when consumers are most vulnerable: often frightened, unable to forgo the product altogether, and dependent on experts in making decisions.

This month the London-based drugmaker Hikma increased the US price of one drug — a liquid form of a diarrhoea treatment — by 430 per cent. The drug is decades old and has no patent protection.

Yet barriers to competition remain. A new manufacturer would need to win regulatory approval and secure production facilities. This is harder for liquid, inhalable, or injectable drugs than for pills. And the new entrant would receive only a fraction of the monopoly price. It is likely a lossmaking proposition.