How To Euthanize Your Cat At Home Painlessly?

Animal euthanasia is the act of putting to death painlessly, an animal which is suffering from an incurable and painful condition. Euthanasia methods are designed to cause minimal pain and distress. It is never advisable or even acceptable to euthanize a cat in your own home. If you have a cat which needs to be put down for any reason, you should take the cat to a trained and qualified veterinarian.
The reason for this is that the cat may not actually need to be euthanized.
Another very important factor is the pain and trauma caused to the cat. If any animal does need to be euthanized it should be done in the quickest and most painless way possible. Therefore, animal euthanasia should only ever be carried out by trained professional veterinarians. 
Pets are almost always euthanased by intravenous injection; the death usually takes around 30 seconds and does not cause the animal pain.  A very high dose of pentobarbital or sodium thiopental is usually administered as it renders the animal unconscious quickly.
A cat or any other pet may need to be euthanized for a number of reasons, such as;
- If it has a Terminal illness - e.g. Cancer
- If it has Rabies
- If it has Behavioral issues that cannot be corrected
- If the animal had lost major bodily functions and was in pain.
It cannot be stressed enough however, that individuals should never take it upon themselves to euthanize an animal. This must be done by a trained professional and in many cases, it is illegal to do so without proper training and licenses.

How many 0.05mg pills of xanax would I require to gently put down my sick 18 year old cat

There are many ways to euthanize an animal painlessly but most are not without dangers,. 

How do people commit suicide? A  car in garage with the engine, does this give anyone an idea, as long as you have oxygen slowly breathing in higher concentrations of anything but will eventually result in unconsciousness. 

I know ether and  another  thing were used to anesthetize patients during ww 1 and the civil war before amputations or surgery. Loss of blood also will result in a relatively painless death. 

Freezing, hypothermia is also an option but believe there is nothing worse than being unfrozen and having frostbite, so all of these things require  firm commitment to a one way trip .

An insulin overdose will result in a diabetic coma. I'd say always have backup

How many 0.05 mg of xanax would it require to gently put down my 18 year old sick cat

Sometimes the vet will come to your house and do that for you. If not I would not just try anything....you don't want to put your cat in any pain that is not necessary.

You can't yourself. It's controlled. You can try to call a mobile vet in the surrounding area if you would rather have that done at home or ask your regular vet if there is a way they can do it.

You should not do that you should take it to a vet