Have Cat Questions? Ask a Cat Vet Online.
Hello. Thanks for the question.
I would stop giving him grass. That can actually irritate the stomach and cause further vomiting. It can also irritate the esophagus and lead to gagging or coughing.
IF there are tapeworms, he'll need to be treated with Praziquantel. This is available through a vet or over the counter at many pet stores.
To help settle his stomach, you could go pick up some Pepcid (Famotidine). You can give 1/2 of a 10 mg tab every 12-24 hours. An alternative would be liquid Maalox or Mylanta- 1/2 teaspoon every 8-12 hours, as needed.
I hope this helps, let me know if you have any other questions.