Wal-Mart, the largest US retailer, has over the past two decades reshaped both the US retail industry and the economy. Can it also reduce the more than $200bn (£100bn; €150bn) that Americans spend on prescription drugs every year?

Since September, the company has been pursuing a high-profile attempt to cut costs, announcing that its in-store pharmacies would sell a month’s supply of 300 commonly prescribed generic drugs for $4, a 60 per cent cut in the cost of the most expensive drugs on the list.