I have been here before with different pets, but why they have all stopped eating is a mystery to me. I have 3 cats and one dog. One cat is in her teens and none have ever had a problem with whatever I fed them. Up to about 6 months ago, I fed the cats one can of canned Friskies, with gravy in the morning, one can split 3 ways. Then in the afternoon, I gave them a bowlful of dry kibble. That worked well for years. However, about 6 months ago, they started skimming the gravy and leaving the meat. So I dropped the canned in the morning and went strictly dry. They had always eaten the dry kibble, but it was going more slowly, so I tried different brands… not much difference. So I have bought 3 different brands of kibble, the one I am feeding now is Wellness. They don’t seem to care for it. I still have a few cans left of the cat food, and I put one out the other day. They lapped up the gravy and left the rest. None are the least bit underweight, and two of them are a little overweight. The old girl has some missing teeth so I hate to put her strictly on kibble, but I have noticed since she has been on kibble alone, she has gained weight!
Now the dog. I did basically the same with him, half a can of dog food in the morning, and kibble at night. He stopped eating the canned, and wouldn’t even touch it. I had been buying Pedigree with gravy until I looked it up on Dog Food Advisor. The first ingredient listed was water! I pulled it immediately and started on Purina One, which had a 5-star review. He ate it better than the Pedigree, but still no gusto. He seems to do better if I stand there and watch him eat. He is nearly glued to my side at all times. I like to order from Chewy and buy a case of dog/cat food at a time, but now I don’t quite know what to do. I took Sam up to TSC to buy some random cans of dog food to see if we could find something he would eat. The cashier was so helpful and friendly. I miss taking my dog there just for the interaction. He is doing a little better, I bought 2 cans of 4-Health, the store brand which is still highly rated. (My former dogs hated it.) and a can or two of other stuff. He is not a fan of most of it. I have NEVER seen a dog turn down canned food. He is not much fonder of the kibble, but at least if it sits out for a couple of hours, it won’t go rancid. He is in great weight, alert, and happy. What to do about this? Any ideas?
The first thing I do when any of my small animals are inappetent is try a course of pepcid. Cats and dogs can develop ulcers just like horses.
Cats, I’ve tended not to hold back and have bought them the most expensive, wholesome additive free canned food out there. They enjoy it at first but soon turn their noses up.
So now they are on Fancy Feast and have reliably eaten it with gusto for many months now. Cheap, Walmart level catfood. I don’t care any more. Eat what you like and I save money 
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Though for both the cat and dog dry food I stick to high end. So far Open Farm is a hit for both.
For canned dog I add some bits of cooked meat, a little mashed squash or pumpkin (from a can, easy to find) or a few blueberries and that gets gobbled.
In my experience animals enjoy variety, just like humans and this keeps them interested.
The two cats I have had that lived the longest at 18 and 19 years ate nothing but Meow mix because I didn’t know any better. My sister who is poor as a churchmouse, feeds the cheapest crap available, as she is also feeding a small colony 
Her house cats usually live into their 20s. She rarely takes them to the vet either. I am not saying that is a good thing, but just weird.
where should I get this? Is there a safe dose for a cat?
Any pharmacy or grocery store with a medication aisle. It’s over the counter. Dose for a “normal” sized cat is 2.5 mg once to twice daily. In your shoes, with how long this has been going on, I’d do twice daily for two weeks, then once daily for another two weeks.
Look for the 10 mg “standard” strength pills.
I prefer the generic (famotidine) from Walgreens because the pills are tiny. Get a good splitter to quarter. It seems to be tasteless and can be powdered to top dress on wet food, although I find 1/4 of the Walgreens pills are so small they really just disappear even without powering. Or use a small piece of pill pocket.
Here’s the dog dose chart.
Yes I’m certainly not advocating to feed low quality food to any animal. I usually lean very far the other direction but was bemused by my cats’ preference for the cheaper canned option.
You can’t really argue with cats : )
