Will a person be held accountable for self-talk and obsessive thoughts that include insulting the Divine, especially if he is taking medication that he believes causes them? And is ghusl (ritual bath), redoing ablution, and prayer required if one remembers taking the medication after praying?

It is not permissible to use tramadol to treat obsessive-compulsive disorder due to the availability of permissible alternatives. Therefore, it does not fall under the criteria that allow the use of narcotic drugs (existence of necessity or urgent need with the absence of a permissible alternative). As for inappropriate thoughts about the Divine Being, if they are merely whispers cast by Satan and you detest them, then there is no sin upon you for them, and they do not invalidate prayer, ablution, or ghusl (definition). You must disregard them and beware of dwelling on them. The remedy for obsessions is to completely ignore them, believe that they are satanic thoughts, and fight them. Maintaining regular remembrance (dhikr) and incantations (ruqya), along with frequent supplication and reliance on Allah, are beneficial in this regard.