Dr. Mehmet Oz promoted green coffee bean extract as a “magic weight-loss cure,” but last week two authors of the study Oz cited in a government hearing retracted their research. In the journal Diabetes, Metabolic Syndrome and Obesity: Targets and Therapy the authors stated that they were unable to assure the validity of the data.

For consumers, it’s a reminder that any supplement should be approved by one’s personal physician before use, Dr. Holly Lofton assistant professor, weigh management program at New York University Langone Medical Center, told FoxNews.com.

In Lofton’s practice, she asks patients to bring in a supplement they’re curious about and she then researches through a medical database to validate the information presented. Then, she reviews the patient’s current medication list to check for possible interactions.

“People respond a lot to advertising or even advice of an ‘expert’ on TV,” Lofton said. “You can’t practice medicine to 2 million people at a time, it really should be done on an individual basis.”

Lack of strict guidelines for supplements allows companies to make claims that haven’t been validated by randomized controlled trials, the gold standard in medicine— and what the Food and Drug Administration (FDA) requires for valid drug studies. Companies may be able to make claims, but their research may not include variables such as a group large enough and diverse enough, among other variables, to extrapolate data into the general population, Lofton said.

The FDA regulates dietary supplement labels and other labeling, such as package inserts and accompanying literature, but does not approve supplements before they go to market. Under the 1994 Dietary Supplement Health and Education Act (DSHEA), companies are responsible for ensuring dietary supplements they produce or distribute are safe, and “that any representations or claims made about them are substantiated by adequate evidence to show they are not false or misleading,” according to the FDA website.

According to Lofton, the FDA acts on supplements retroactively— if, for example, a supplement caused a health problem with a group of users— rather than proactively before the product is put on the market.

“I think that’s a little bit backward,” she said.

The FDA declined to comment for this article.

FoxNews.com reached out to Generation Nutrition Corporation (GNC) but the company does not comment on industry studies, a representative said in an email.

Lofton also noted that supplement companies create “proprietary blends” of ingredients to avoid copying by competitors, but those “blends” don’t always disclose actual ingredients or quantities of listed ingredients.

“Essentially, you don’t know what’s in these,” she said.

While some supplements, especially those marketing themselves as originating in natural sources, may seem harmless, consumers need to think twice.

“People take [supplements] to be a benign substance— ‘[It’s] not even as bad as aspirin because I have to talk to your doctor about it but I can take this off the shelf. It must be just like eating a cookie’— but it does have a risk, you’re putting chemicals in your body,” Lofton said.

While prominently featured doctors with television shows may include disclaimers that their shows aren’t meant to substitute medical advice, Lofton noted that it’s important to remember that the shows are meant for entertainment and aren’t meant to give you advice to take for the rest of your life, such as changing or adding a medication.

“Taking advice with good intention from a doctor on TV may end up doing self-harm because you didn’t run it by the physician who knows you very well,” she said.

Anyone considering taking a supplement— especially those with diabetes, high blood pressure and any heart condition— should first consult their doctor to ensure there are no potential side effects related to existing health conditions or medications. Lofton cited the supplement OxyElite— one of GNC’s most popular products— which was investigated by the FDA in July 2014 after consumers developed non-viral hepatitis.

As for a real “magic weight-loss cure,” that would be impossible, Lofton said—there are too many factors to find one specific pill, injection, or procedure that would treat all issues that contribute to weight gain.

“I would say anything touted as a ‘miracle’ I wouldn’t take that to heart unless the person has ‘Saint’ in their credentials,” she said.