I wonder if there are any natural meds which can be used when cat suffers from flu. I have no problem to buy meds for them, I just want to know if there is any alternative. Once my cat had a hoarse voice and one Vet suggested honey on the paw, which I gave to her and it was everything ok.
"Flu like" upper respiratory symptoms in cats can be caused buy a variety of viruses, some dangerous and requiring veterinary attention, others fairly harmless and will pass in time just like the common cold for humans.
If your cat appears to be ill with flu-like symptoms, a diagnosis from the vet is required to know if it's a flu/virus that will pass, or a bacterial infection like kennel cough that needs to be treated with antibiotics.
Generally the home treatment for all the cold-like or flu-like diseases of cats is just supportive treatment: Make sure the cat is kept warm enough, fed and hydrated (by temptation, such as with warmed, soft or especially tempting foods, unsalted broths, etc, or by force or even IV line if it comes to that). You may also clean the nose and eyes gently with saline or salted water, and let your cat stay in a bathroom with the shower running on hot so steam can loosen the mucus. A humidifier can also help, but ensure that it is kept very clean and away from the cat's reach. DO NOT use any sort of essential oils, mentholated topical products like chest rub, or scented diffusers, many of these contain ingredients that are dangerous for cats, even if they are considered mild and safe for human use.
Here's some additional information about the cat flu.