Fortisip Extra Fortisip Extra is a nutritional supplement specially formulated for people with increased nutritional requirements. Fortisip Extra is a high energy & high protein milkshake style drink that contains 50% of the reference nutrient intake (RNI)* for vitamins & minerals in one convenient, ready to drink bottle. Fortisip Extra is not suitable as a sole source of nutrition & should be taken under medical supervision. Fortisip Extra comes in a 200ml bottle, with a flexible straw attached & is available in 2 flavours: Vanilla & Strawberry. Simply choose your favourite flavour (s) from the drop down menu above.