What is the brand name for the drug used primarily for the treatment of irritable bowel syndrome?

The drug primarily used for the treatment of irritable bowel syndrome (IBS) is known by the brand name Bentyl. Bentyl, whose generic name is dicyclomine, is an anticholinergic medication that works by relaxing the muscles in the gut, which helps to alleviate spasms and cramping associated with IBS.

In contrast, the other options are utilized for different medical conditions. Amaryl, for instance, is used to manage blood sugar levels in individuals with type 2 diabetes. Celebrex is a nonsteroidal anti-inflammatory drug (NSAID) effective for pain relief and inflammation, but not specifically for IBS. Novolog is an insulin used for controlling blood glucose in diabetes, which does not relate to gastrointestinal issues. Thus, Bentyl is specifically indicated for treating the symptoms of IBS, making it the correct answer in this context.