By some estimates, about 90% of all prescriptions in the U.S.

Are filled with generic drugs.

Insurance companies encourage their use over brand-name medications to reduce health care costs.

The fda says that all agency approved generic drugs have the same high quality strength, purity, and instability as brand-name drugs but a pro public at investigation found that the fda rarely tests the quality of generic drugs.

Many of the manufactured overseas.

Our national reporter was one of the authors of that investigation.

The fda does not test these drugs but you independently tested some of the most widely use generic drugs.

What did you find?

Reporter: The fda is not regularly testing drugs.

What we found in the testing is that there were certain versions of widely prescribed generic drugs that have concerning results because they did not dissolve properly in the body.

John: Have patients or other people expressed concerns about this in the past?

>> Absolutely.

This is one of the reasons we did the testing in the first place.

Because doctors, pharmacists, consumers, academic researchers, even the department of defense has raised concerns about the quality of some of our generic drugs.

Despite all of that the fda does not have a regular testing program.

The agency does not regularly test for quality and safety issues.

John: Do they do that with brand-name medications?

Reporter: No, the fda publicly reports the names of the drugs they test but there is no regular testing program.

They say they test based on risk but what we found it is they are not regularly testing drugs coming in from some of the most troubled factories overseas.

John: What is the fda's rationale for this?

Reporter: They just did not think it would work right because they would only be testing a sample.

A small sample.

A moment in time.

They were not necessarily pick up on trends.

And wider concerns.

But the department of defense is now testing over 40 drugs because they are concerned about contaminants and other things I can go wrong.

Not all generics are the same as brand-name drugs.

Doctors and patients have been saying that for years.

John: Talk about what patients have been saying.

Have there been specific cases where people have said that the generic does not feel the same as the brand-name or they wonder about the effects?

Reporter: Absolutely.

That is what struck us as reporters.

How many people turn to social media and say something is not right with this drug.

One of the drugs we have tested was an antidepressant.

So many people said for so many years that when they switch from the brand of wellbutrin to a generic or one version of the generic to another, they get all kinds of funny symptoms or worse.

They feel the drug is ineffective.

Doctors might say that something is wrong, it is just you or it is your body or it is mother nature or it is bad luck.

But it actually might be that that version of that drug does not work the same as the brand.

For too long we have not really been asking those questions.

John: In addition to testing these generics yourself, you also created a tool where people can check what is in their medicine cabinets.

Tell us about that.

Reporter: We really wanted to empower consumers to take control of their own health care.

By creating a tool where you can actually take the information on the labels of your pill bottle and stick it in this tool and think about where you drugs were made.

The factory that made it and whether that factory has ever been in trouble with the fda for substandard manufacturing processes.

John: Where do people go to get this tool?

>> On the website of pro public code.

We are free.

It is important to note that even if you find something, a bad inspection for a factory that makes your drug, that is not necessarily mean that you're generic is unsafe and you should stop taking the drug.

You should always talk to your health care provider.

We really felt that this was information that had never been made public before.

Not by the fda and not by the drugmakers themselves.

So we spent many months putting this tool together for consumers.

John: Thank you very much.

Reporter: Thank you for having me.

John: Still to come, how social media can affect people on the move around the globe.

And a new technology that is helping scientists better understand monarch butterflies.

♪ >> This is pbs news weekend from our studio in Washington, home of the news hour weeknights on