Im sorry to hear about your problems with chronic constipation. No chronic constipation can be due to severalunderlying causes. You have mentioned that you have undergone several tests however you did not mention whether a colonscopy has been done or not. If it has not been done as of yet, that would be the first step in determining the underlying cause for this constipation. There are several intestinal disorders which can cause this problem such as an intestinal stricture which can obstruct the passage of stool. Secondly any masses or growths inside the abdomen can also cause this sort of constipation.
if this has been done already and the colon has been excluded as a cause then we can consider IBS as a cause for your constipation. Many people think of irritable bowel syndrome as causing diarrhea only when the fact is it can cause constipation as well. if this is the case then changing your dietary habits,liking increasing fiber in your diet which you are already doing can be helpful. Secondly use of metamucil and benefiber may be beneficial here as well as several drugs.
Regarding the hormonal causes, one thing which can be checked for is hyperparathyroidism which can cause chronic constipation as well. This would have to be checked for particularly and can also cause your calcium levels to be higher than normal as well.
Now the constipation can also be the result of the drugs which you are on, of the drugs which you are using, the following can cause constipation.
Risperidone (in upto 10% of the patients)
Gabapentin (in upto 5% of the patients)
It is possible that the combination of these medications is causing you the constipation.
Now the solution here can be the increase in dietary fiber, regular use of supplementary fiber or use of medications to improve the constipation. You might benefit from the use of amitza which is recommended by FDA for use in chronic constipation of unknown cause. Linzess can be another option here.
Now i would recommend that you talk to your doctor regarding these options
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