I'm looking at the side effects of Madopar, and all of them are listed as "unknown frequency".
How can frequency be unknown? Even if just one of a million patients got a certain side effect, that just means that frequency is 1 millionth, right?
The only reason I can think of, is that zero side effects occurred in the drug's clinical test, AND people contacted the company about their side effects AFTER the drug was already on the market. That seems unlikely, though.
I found this link but it's a bit of a wall of text.