You’re grumpy, and you wonder why. So you enter the word in a symptom checker online and find out you may have one of 82 disorders or diseases, ranging from a middle ear infection or menopause (and you’re a guy!) to dementia or a subarachnoid hemorrhage between your brain and the tissue that covers it.

Try again.

You also have achy joints. Ah, that leads you to a list of 101 causes of joint pain. Maybe it’s ulcerative colitis-related. Who knew it could make your joints hurt? Or from infectious mono? That wasn’t a good date!

But you cannot find any condition that shows up on both lists. So maybe you have two different illnesses at the same time!

That can be an information-seeker’s nightmare. Yet hundreds of millions of times a year people turn to online and app-based symptom checkers to help figure out what’s ailing them, and if they should call the doctor or if it’s time for a visit to the emergency room pronto. You might as well ask a crystal ball.

That’s the conclusion of a recent study in The Lancet that examines both the promise and reality of symptom checkers. The researchers looked at a wide range of studies on diagnostic direct-to-consumer digital tools and concluded: “Overall, the current evidence base on direct-to-consumer, interactive diagnostic apps is … uneven in the information provided and inconclusive with respect to safety and effectiveness.” Buyer beware, for sure.

This reinforces findings from earlier studies: While misdiagnosis by human doctors happens about 5 percent of the time, affecting about 12 million U.S. adults annually, according to a 2014 study in BMJ Quality & Safety, misdiagnosis by digital symptom checkers happens, on average, about 50 percent of the time!

In another study published in BMJ in 2015, researchers tested 23 symptom checkers by having them evaluate symptoms derived from 45 clinical vignettes that are used to teach and test medical students.

Overall, the symptom checker listed the correct diagnosis first in only 34 percent of cases and put it in the top three diagnoses 51 percent of the time. And another study published in 2015 in Diagnosis concluded, “research suggests that (medical apps and online tools) should be used with great caution … The lack of verifiable information provided about the evidence or expertise used to develop these apps is of major concern.”

GET SMART

You’re not going to stop checking out online health info — and shouldn’t. But all symptom-checker digital health sources are not created equal.

1. A reliable symptom checker was developed for the Department of Defense and is available on the free Sharecare.com app. We feel it’s the best one, but we helped develop it so we may be biased. It offers the questionnaires and data, and is likely to offer correct diagnoses. Plus, it will send you to a nearby doc (or telemedicine connection), if you want one.

2. Telemedicine can provide personalized medical advice reliably. Check what is available at your local medical institution.

3. Don’t let online results make you think you can determine your own treatment. You know the expression “a lawyer who represents himself has a fool for a client”? Well, a patient who has himself or herself for a doctor is foolish, too. Get your online info, then call your local or telephysician for a consult and/or an appointment.

4. As for online health info: We hope you’ll use it to help you stay healthy so that you don’t need a symptom checker. But you can find reliable health information at RealAge.com and DoctorOz.com — trustworthy zones where you can get the support, encouragement and advice to be your healthiest self.

Mehmet Oz, M.D., is host of “The Dr. Oz Show,” and Mike Roizen, M.D., is Chief Wellness Officer and Chair of Wellness Institute at Cleveland Clinic. Email questions to youdocsdaily@sharecare.com.