Hi Dr Sudhir, Welcome to HCM! Thanks for posting your query. I am happy to address your questions. Various iron salts will have different proportion of elemental iron being absorbed in the body. It depends on inter-subject variability. Choice has to be made based on requirement of iron as well as better absorption of iron with minial side effects. Some patients do not have any issues with sulphate, fumarate or ascorbate salts whereas some may have - so the form of Iron is tailored at the beginning. Answering to the above question, ferrous ascorbate has better absorption profile with less side effects (though elemental iron supplied to the body is comparatively less). Many people using this medication do not have serious side effects other than GI nausea and constipation. A very serious allergic reaction to this drug is rare. However, as allergic reaction can occur in different patients without any prior concerns in the form of edema, rash, severe dizziness, trouble breathing, would recommend to seek medical intervention. Hope I have answered your query. If you have any further questions, I will be happy to help. Thanks