Iron is safe for consumption as it is a nutrient that is already present in us. Iron is found in the haemoglobin of red blood cells and is required for transporting oxygen and carbon dioxide.
When taken by mouth in appropriate amounts, it is mostly safe but can however cause side effects. The most common side effects are gastrointestinal (GI) disturbances like nausea and constipation.
There are many forms of iron supplements and different forms affect different patients differently. Taking supplements with food seems to lessen its side effects however caution is needed not to take your iron supplements with dairy products, coffee or tea as this may impair absorption.
Therefore taking iron via injection which bypasses your GI tract instead may be a more effective way of correcting your iron deficiency and preventing anaemia, which will develop.