Are you allowed to voice concern(have a disagreement) with your parent if the topic is related to their health or well-being? Is it wrong to send them information that supports your view but contradicts their opinion? Or must you always agree about everything in order to honor them?
The mitzva of kibbud av v’em has two main parts, to honor (kibbud) and to revere (morah) our parents. Honoring a parent, entails things that we do (say, or think) that are positive to our parents. Revering on the other hand are the things that we abstain from doing in reverence to our parent. One of the things included in morah, is “lo yistor es divarov” not to contradict what the parent is saying. Examples of this are:
- A child may not say to his parent, ” that’s not true”, even if he knows it isn’t true.
- If one’s mother is saying a story, the child may not say, “that’s not what happened” or “better say it like this…”.
- A son accused of doing something wrong should not say, that’s not true, rather, “I have what do defend myself with…”
- Or if asked by a parent to check over their books, don’t say, “You made a mistake”; rather “this is incorrect”.
When discussing Torah topics, and this would include discussing something related to the parent’s health, a child may also not contradict his father by saying, that’s not true, etc. He may however bring proofs against his father’s opinion, which obviously shows his opinion on the matter. If, at the end of the conversation the son still disagrees, he should not tell this to his father specifically.
 Rabeinu Yona Sefer Hayirah.
 Sefer Hamussar of Horav Y. Kaletz brought in Yalkut Yosef (Kibbud Av v’em)5-35..
 Ben Ychabed Av pg. 91.
 Morah Horim Vkibbudam 3-12.
 The Shuchan Aruch Y:D 240 and poskim do not differentiate between discussing torah topics and other topics, that when discussing torah topics is still not allowed to outright contradict the parent.
 Atzmos Yosef Kiddushin 30b, brought in PIskei Teshuva Y:D 240-1, Aruch Hashulchan Y:D 240-9.