Biologically, cats are very unlike humans. Just looking at their reflective eyes with vertical pupils should be enough to remind us of that!
The ancestor of the domestic cat is a species of wild cat found in the deserts of Egypt, Israel, Jordan, and Syria. These animals were domesticated by farmers who realized their value in controlling grain destroying pests such as mice and insects.
Cats are still very much desert creatures. They can go for long periods of time without eating or drinking, as is confirmed time and time again when an unfortunate cat is forced to make an involuntary cross-country journey on a truck or in a shipping container. All cat owners are familiar the highly concentrated feline urine, which is indicative of how efficiently cats process and conserve water.
Medications are very often species specific. Similar species can quite often benefit from the same medication, but the more different two species are, the more unlikely it is that they can share the same medications.
Given the great differences between cats and humans, human medication should never be given to a cat unless specifically prescribed by a veterinarian. The risk of causing further harm or even death to the cat are just too great.