Medicines Yes, you read it right! Some medicines also cause constipation. For example, anti- depressants or anti- anxiety, pain killers, cholesterol lowering agents, antacids, blood pressure medicines, iron supplements lead to constipation. Hence, your medicines should be consulted with your doctor and then taken for no side effects. Constipation is the most common side effect of medicines when taken in a large dose or when such medicines are taken as described above. It may be necessary to take those medicines, in that case it should be supplemented with an increased intake of fluids. Also, increase your fibre intake via fruits and vegetables or flax seeds have also proved helpful.