Weight loss, loss of appetite, and lethargy in cats may be caused by the following reasons:
Disease factors: such as colds, gastrointestinal diseases, parasitic infections, etc.
Oral problems: Tooth pain or oral inflammation may lead to a decreased appetite.
Dietary issues: unsuitable food, spoiled food, or food that you don't like to eat.
Stress and anxiety: changes in environment, the appearance of strangers or other animals, etc.
Endocrine problems: such as hypothyroidism.
Digestive system problems: indigestion, gastrointestinal diseases, etc.
