Olfen 100 SR is the brand name of a pain-killer called diclofenac sodium 100mg. It should be avoided in people with high blood pressure and other heart diseases, though it is not totally prohibited in these conditions. It should be taken before meals.
It's side effects include: nausea, tummy ache, headache, retention of water in the body (oedema), dizziness, skin rash etc. There are other rare side effects.