It literally says that in the article. Just, apparently, further down than you read:

MODAFINIL WAS DISCOVERED in the 1970s by French scientists and was first handed out to pilots to help keep them awake and on task in the 1991 Gulf War. The U.S. military started to use modafinil in earnest around the 2003 invasion of Iraq. At the time, it was heralded as a massive improvement over previous stimulants: stronger and more effective than caffeine, less physically addictive than amphetamines. “These medications aren’t stimulants like the old military ‘go pills,’ there are few if any side effects when taken as prescribed. They simply stave off drowsiness until the medication wears off, then you naturally fall asleep,” one knowledgeable source writes.

But that “taken as prescribed” caveat is crucial. When handed out willy-nilly, outside a doctor’s supervision, modafinil can pose serious risks, notes Dr. Rachel Teodorini, a researcher at London South Bank University’s division of psychology who has examined the drug and its effects. “If people have cardiovascular problems, heart problems, or blood pressure issues, it could cause things like strokes or heart attacks,” she tells us. And while modafinil doesn’t appear to physically hook patients, “there’s an element of at least psychological dependence. Tolerance builds up, and you need more and more.”