The bank described this form of debt as "a tool used by stock speculators to borrow money from brokerages to buy more stock than they could otherwise afford on their own. If the stock rises, they end up making far more money. If the stock crashes, the opposite materialises. This kind of speculation is highly alarming."
The bank warned that forced sales of stocks can set off panic and a rush for exits, snowballing into a crash, as happened in 1929. It said the equity rally may have further legs but it cited "astonishing similarities" between the latest patterns and events preceding prior market crises.