The primary objective of this study is to assess the potential of linaclotide treatment to induce the development of anti-drug antibodies (ADAs). The secondary objectives are to provide additional evidence supporting the long-term safety and efficacy of linaclotide in adult irritable bowel syndrome with constipation (IBS-C) and chronic idiopathic constipation (CIC) patients and to evaluate lower doses of linaclotide.