The use of nutritional supplements (ready-made drinks or powders which are mixed with water or milk) is not the ideal way to manage unexpected weight loss and should only be considered when other ways of getting the nutrition we need through food has failed.
The Food First approach of eating small but frequent, high energy, high protein snacks and meals is the best option for older people because it also acts to maintain teeth and bowel heath.
If you do need to use supplements, the highest quality are those prepared by dieticians for hospital patients. Products such as Sustagen Blue - it will provide 945kJ and 13.8g of protein for a $1.80/serve. Revival’s range of protein drinks are available from most supermarkets and will give you about 1100kJ and 30g of protein per serve for about $4 for 375ml.
Depending on your situation, some of the powdered supplements may be subsidized if recommended by your doctor, so check with your GP.
The use of more concentrated protein supplements should also be under the direction of your doctor as they affect your medications.
A number of studies have found older people who have unintentional weight loss are not only need more protein and kilojoules but also need vitamins and minerals. If you have lost weight without trying, any supplement should be targeted you and directed by your doctor. While a multivitamin might not do any harm, it may not be the best solution for you. Speak to your doctor.