These are given to patients with anaemia due to a deficiency of iron.  They are usually prescribed when a trial of iron tablets has been unsuccessful, either due to side effects or malabsorption.  The iron solution is given through an intravenous drip placed in your hand or arm.  The rest of the dose is then given over one to six hours, depending on the dose prescribed for you.  Possible side effects include headache, vomiting, muscle aches and flushing.  Rarely, more serious reactions may occur such as difficulty breathing, low blood pressure, and collapse.  Sometimes these reactions can be stopped by slowing down the rate of the infusion, or more rarely stopping it.  Very rarely, drugs may be given to treat the reaction.  Once the iron is replaced, the body starts making more red blood cells within the next two weeks.