user1413: To one of my questions I received an answer that I believe is partly wrong (see the comments). I felt that discussing the issue with the author of the answer was the right way, but I open it up here.
John claimed that "a laxative should increase … transit time", but I don't believe this and I found a counter-reference, asking him to support his statement.
It wouldn't be unique even for high quality scientific literature to include contradictions. So if he underpinned his statement with a reference I would find it interesting and helpful. But if he does not? Shall I downvote his answer? After how long if he does not reply?
Shall I edit his answer to my question and remove the parts that seem to be wrong? How to do this without offending him?
What to do in general when a statement does not seem to be true?

user6: Don't edit the post in cases where you disagree with the original author. You did the right thing by commenting on the point that you are skeptical about. 
Your next possible steps are to downvote if you consider the answer to be wrong. If you have the necessary knowledge to write a better answer you should write one containing a correction of that issue.
Usually there is not much more you can do, moderators in general don't decide on the correctness of an answer and would not intervene in this case. 

1413: <p>To one of my questions I received an answer that I believe is partly wrong (see the <a href="https://biology.stackexchange.com/questions/8808/why-do-antibiotics-have-a-special-importance-when-taking-lactulose/8830?noredirect=1#comment11354_8830">comments</a>). I felt that discussing the issue with the author of the answer was the right way, but I open it up here.
John claimed that "a laxative should increase … transit time", but I don't believe this and I found a counter-reference, asking him to support his statement.</p>

<p>It wouldn't be unique even for high quality scientific literature to include contradictions. So if he underpinned his statement with a reference I would find it interesting and helpful. But if he does not? Shall I downvote his answer? After how long if he does not reply?</p>

<p>Shall I edit his answer to my question and remove the parts that seem to be wrong? How to do this without offending him?</p>

<p>What to do in general when a statement does not seem to be true?</p>
 6: <p>Don't edit the post in cases where you disagree with the original author. You did the right thing by commenting on the point that you are skeptical about. </p>

<p>Your next possible steps are to downvote if you consider the answer to be wrong. If you have the necessary knowledge to write a better answer you should write one containing a correction of that issue.</p>

<p>Usually there is not much more you can do, moderators in general don't decide on the correctness of an answer and would not intervene in this case. </p>
