For most people ingesting cantaloupe does not cause diarrhea although sometimes it can, especially if the person has an allergy to this fruit. There are other symptoms to watch out for with regards to an allergic reaction, including gas, vomiting, and upset stomach, although these reactions are fairly rare.
Another reason why someone might be getting diarrhea as a result of eating cantaloupe is because they have left it sitting out too long without freezing or refrigerating it. Even after a couple days in the refrigerator cantaloupe can start to go bad, so it will be extremely important to make sure that it is properly stored and consumed within a reasonable amount of time.
If you are not going to eat it within two or three days of getting it from the super market, it is recommended that you freeze it in a vacuum-sealed bag.