If u dont mind me asking, what is the reason the vet prescribed it?
Metacam does have side effects but short term use is usually ok unless ur pet reacts badly (dog/cat) this usually happens within the first 12hys of using it, most common is vom n diarrhoea.
If u want to play it safe and use holistic painkillers there are a few out there...arnica, green lipped muscle or long term use of glucosamine,chondroitin and msm is good for maintaining joint health, if its an arthritic condition.
good lk