Irritable bowel syndrome is a group of symptoms that includes abdominal pain and changes in the form and frequency of stool. Since its symptoms are usually long-lasting, the disease significantly degrades quality of life. Several pharmacological therapies have been suggested according to the type of symptoms (e.g., abdominal pain, constipation, or diarrhea). In order to control abdominal pain, smooth muscle antispasmodics, antidepressants including tricyclic antidepressants and selective serotonin reuptake inhibitors, or 5-HT3 antagonists can be used. To improve constipation, dietary fiber or laxatives, 5-HT4 agonists, and chloride channel activators are available. Opioid agonists, mixed opioid agonists/antagonists such as eluxadoline, and bile salt sequestrants can be considered for diarrhea. In addition, probiotics and non-absorbable oral antibiotics can be used for the normalization of the gut microbiome and the treatment of small intestinal bacterial overgrowth, respectively. It is necessary to understand the characteristics of each drug and their combinations, because any single regimen cannot improve all symptoms in patients with irritable bowel syndrome. In this review, the mechanisms of action, efficacy, and adverse events associated with drugs used for irritable bowel syndrome are summarized.