Brief Answer: due to mechanical trauma Detailed Answer: HI, thanks for using healthcare magic The insertion of the tube or scope used in gastroscopy could cause temporary minor trauma to the pharynx ( this is part of the throat). The trauma would cause sore throat that can generally last 24 to 72 hours. Coughing generally occurs due to stimulation of cough receptors in the body. Some of these receptors are found in the pharynx. They can be stimulated by mechanical trauma (such as the gastroscopy) or chemicals (acid, heat, some medications, mucus, infection). This response should also resolve in the time mentioned 24 to 72 hours. There are gargles that may be helpful in relieving the discomfort in the throat such as chloroseptic, covonia, diflam. He may want to consider the short term use of an over the counter cough suppressant to decrease the coughing. EG robotussin I hope this helps , feel free to ask any other questions

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