Wait until each has regained its composure to feed it. Try again the next day. As things settle down, allow them to spend progress ively longer periods together after they have eaten each meal. Move their food dishes gradually closer to each other at successive meals. If problems occur at any time during the introduction process, return to the preceding step as outlined above.
Some cats are less sociable toward others and less willing to share their territory.
If the cats are consistently aggressive toward each other, it may be necessary to sedate one or both cats. Psychoactive medication should be prescribed by your veterinarian and used only if necessary and for a short time. Both cats are likely to experience some anxiety during the transition period, though one cat will likely react more strongly than the other. Unless there is a medical reason not to use medication or one cat seems completely unbothered by the other, both cats are likely to benefit from medication. With time, most cats learn to accept others in the household.