This is a Phase 2, randomized, open-label, parallel-group, multicenter study designed to evaluate the safety, pharmacokinetics, and efficacy of paltusotine treatment in subjects with carcinoid syndrome. The study was conducted in 2 parts: a Randomized Treatment Phase (RTP) which is completed, and an Open-label Extension (OLE) Phase which is still ongoing. The RTP consisted of paltusotine treatment for 8 weeks. Subjects who completed the RTP were eligible to enter the OLE Phase at the recommendation of the Investigator. In the ongoing OLE Phase, paltusotine is being administered for a further 102 weeks. The total duration of paltusotine treatment for the combined RTP and OLE Phase is up to 110 weeks (28 months).