At the first signs of the flu (fever, chest pain, body chills) you might spend a good hour or two consulting with Dr. Google about what drugs could help. Or not. Let’s face it, the flu renders almost everybody useless, and you probably feel miserable enough to take just about anything.

Odds are your doc will prescribe one of three antiviral meds: inhaled zanamivir (brand name Relenza), intravenous peramivir (Rapivab), or oral oseltamivir, otherwise known as Tamiflu. Of those three, we’re willing to bet you get a script for Tamiflu. Not only is it the one your friends have heard of, it’s also the only one that made the World Health Organization’s list of essential medications.

But Tamiflu has been the subject of controversy in recent years—which has left many wondering, How are you supposed to know when it’s worth taking? With flu season still in full swing, we’ve gathered the facts on this pricey drug so you can weigh the pros and cons before you’re too achy to think straight.

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How well does Tamiflu work?
A 2014 review by the Cochrane Collaboration, an independent network of researchers, found that the drug did not reduce hospitalization rates for the flu, and only shortened the duration of people’s symptoms by 17 hours. But 17 hours isn’t nothing when you feel totally terrible.

It is worth noting that the study authors expressed some doubt about their findings: “We identified problems in the design of many of the studies that we included, which affects our confidence in their results.”

As for flu prevention, the Food and Drug Administration says Tamiflu can also keep people from getting sick in the first place.

Can I skip the flu shot and take Tamiflu instead?
Nope—the drug is not a substitute for early flu vaccination, according to the drug’s manufacturer. Getting a flu shot is the best way to prevent the flu. Your protection lasts through the entire season. Plus, Tamiflu is expensive. Consumer Reports quoted the cost of a 5-day course as at least $100.

RELATED: Another Surprising Reason You Should Get a Flu Shot

Who should take it?
Tamiflu is approved to treat influenza in people whose symptoms have not lasted longer than two days (which might come as a surprise to anyone who has gotten a script after being sick for a week.)

“The literature on antivirals for influenza shows that they work best when taken 48 to 72 hours after the onset of flu symptoms,” explained Dr. Susan Rehm, vice chair of the department of infectious disease at the Cleveland Clinic. If your take antivirals after that window, “the potential benefits are less,” she notes.

That said, doctors might prescribe Tamiflu to people who are immunocompromised or at risk of flu-related complications, even if the 72-hour period has passed, Rehm said.

“Even healthy people may develop complications of influenza, like bacterial pneumonia,” she said. (If you have a fever or shortness of breath that lingers, alert your doctor, Rehm urged.)

RELATED: 10 Biggest Myths About the Flu

Should I be worried about resistance to Tamiflu?
According to the Centers for Disease Control and Prevention, “antiviral resistance to oseltamivir… among circulating influenza viruses is currently low.”

The bottom line?
Whether you take Tamiflu or not is up to you and your doctor. No one should take any drug unnecessarily, Rehm pointed out. And the side effects of Tamiflu—which include nausea and vomiting—are worth considering. But, she said, among her patients who have decided to take Tamiflu, “many comment that they seemed to have recovered more quickly.”

This article originally appeared on Health.com.