It kind of sounds like a situation I had with my cat. I noticed she was losing weight despite eating a lot more so I wormed her. That didn't do anything so I had to take her to the vets and she had an overactive thyroid. I'm not at all well off (I only work part time and I'm part time carer for my mum) but I managed to scrape the money together for a blood test which confirmed the thyroid problem. It does seem to be more common in older cats.

If the worming doesn't work, definitely take your cat to the vet would be my advice. Hope he improves soon. xx

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Owned by Ratty girls Hera, Athena, Boomer and Kitty the Cat
RIP Apollo and Starbuck, together again at the Rainbow Bridge. Till we meet again.