How can I help my cat gain weight?

What can I supplement my cat's diet with to help him gain weight? He is 16 years old and losing small amounts of weight each time he is weighed. He has been screened for hyperthyroid, kidney and other problems and is fine. My vet suggested he just has age related muscle loss. He is on a prescription diet for bladder stones so I can't really change his main food, I'm just looking for an at home suggestion to help him fatten up a little.

Try feeding him a daily dose of glucosamine- chondroitin. I had an old cat with arthritis & this stuff did wonders for her.
   
It's mainly for joints, but it will likely help build up her muscles too, as she may be losing muscle because it hurts to walk around, so she's not getting enough exercise to build up the muscles.
   
The brand & size you want is Regular form: "Cosequin Sprinkle Capsules for Small Animals", (Glucosamine 250 mg, Chondroitin 200 mg, Vitamin C 16 mg, Manganese 2 mg)
   
It's the white bottle with the hairy terrier dog.
   
Dosage is 1 tablet per day for cats.
   
They have Cosequin for Cats, but it's less expensive in this bottle & it works the same.
   
You can surf for the best prices. EntirelyPets is a good website; also DrsFosterSmith. I personally avoid "1800PetMeds", I don't trust them, & the online criticism of their operation is pretty withering.
   
The Cosequin takes a few weeks to show a real effect, so be patient.
   
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