LONGECITY

If you have IBS or celiac disease, you have problem absorbing in small intestine where pretty much everything orally is absorbed . I read that niacin is absorbed primary in the small intestine but some also in the stomach. Or coconut oil which is absorbed directly into the liver. SO are there any vitamins or minerals or even supplements or drugs that when taken orally have a different route and are not absorbed in the intestines? etc this could be helpful / beneficial if you have absorption problems there. as well with vitamin c  and nac