Antibiotics transformed medicine in the twentieth century, turning once-fatal infections into routine ailments. Today, however, their success carries a hidden cost. Every time an antibiotic is used, a few bacteria may survive because of chance mutations, and these survivors multiply while their weaker neighbors die. Over time, the population becomes dominated by resistant strains. This process is not a flaw in the drugs but a basic feature of evolution. What can be changed is the speed. Studies show that a large share of antibiotic prescriptions for mild respiratory illnesses are unnecessary, since many such illnesses are caused by viruses, against which the drugs are useless. Farms add to the problem by giving low doses to healthy animals to promote growth. Reducing unnecessary use is therefore the most direct strategy, but it is not sufficient on its own. Developing new drugs is expensive, and companies earn little from medicines that doctors are told to use sparingly. Some economists propose that governments pay firms a fixed fee for developing effective antibiotics, regardless of sales volume. Without such a change in incentives, the pipeline of new drugs may continue to dry up.

In the passage, "sufficient" in "it is not sufficient on its own" most nearly means: