Researchers in Georgia found that survey respondents tended to expect their cough to be gone in about a week, but a review of cough studies shows the hacking takes about three weeks to clear up.
The team writes in the Annals of Family Medicine on Monday of their concern that people's unrealistic expectations may lead them to ask doctors for antibiotics that won't speed their recovery, but will fuel drug resistance, cost money and increase the risk of side effects.
"We're not trying to discourage people from getting care if they feel they need it, but at the same time we want to give them the confidence to give themselves care in situations when it's appropriate," said Dr. Mark Ebell, from the University of Georgia in Athens, who led the work.
For the new study, Ebell and his colleagues took a telephone survey of 493 adults in Georgia about how long they'd expect a cough to last based on a hypothetical situation.
For example, they asked how long a person would expect their cough to last if they had a 100.5-degree fever and were bringing up yellow mucous.
Overall, people said they'd expect their cough to take between 7 and 9 days to clear up.
The researchers then reviewed 19 previous studies on severe coughs that recorded how long the condition actually lasted.
In those studies, it took a cough - on average - 17.8 days to subside.
"I think it is important to understand that if you do get a cough you're probably going to be coughing for about three weeks," said Dr. Jeffrey Linder, who was not involved in the new study but has done similar research.
"Also, there is evidence out there that getting an antibiotic at any point in the course is not going to make it shorter," said Linder, an associate professor at Brigham and Women's Hospital and Harvard Medical School in Boston.
The gap between how long people expect their cough to last and how long it actually does may drive some to the doctor for antibiotics that won't help, according to a new study.
According to the researchers, about 50 percent of patients diagnosed with an acute cough in 2006 were prescribed an antibiotic. But most respiratory infections are caused by viruses - while antibiotics only affect bacteria.