People quite reasonably expect drugs and medical devices to meet some level of safety and effectiveness. The trials and regulatory approval process exist for this purpose. However (and there is probably no way around it), that means that there is a relatively high barrier to entry that delays or discourages the entry of new competitors into the market, even when a “greedy monopolist” situation would ordinarily invite new competitors to enter the market. That is in addition to any patents that may exist, of course.
The other difference in the market for drugs and medical devices is that, for many such products, the users do not have as much choice to go without. In monopoly situations involving optional purchases, people who think that the price is too high just do not buy. But people who need to carry epinephine for life threatening allergy risks are less likely to want to risk going without an auto-injector.