Brief Answer:
Possible higher dose-to-body weight effect

Detailed Answer:
Dear XXXX,

Thanks for posting on this forum and I am pleased to be able to assist you.
I understand your very disturbing concern. It is true that majority of the time medications respond to its specific needs but reasons (most at times) we cannot possibly explain they may react differently to different people. In your case, you are experiencing a rare adverse effect of muscle stiffness or cramping induced by Flexeril. Sure you may be wondering how this is possible but this is just one of the mysteries of how drugs work on different humans. You should not be worried, though, it does not mean you have any specific problems of concern. According to the manufacturers, there is no known interaction between Flexeril and Zontivity.
I suggest if the effects persist, you should call your doctor immediately. In any case, you can withdraw the medication temporary then observe to see if any changes (as a temporary measure).

Hope this helps and best wishes.
Dr. Nsah

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