The FDA lists the following:For subjects with chronic idiopathic constipation taking Amitiza:

Nausea ~ 29% (4% were severe, and 9% of patients discontinued treatment due to nausea. The rate of nausea was lower among male (8%) and elderly (19%) patients. No patients in the clinical studies were hospitalized due to nausea.) Diarrhea: ~12%  (2% were severe, and 2% of patients discontinued treatment due to diarrhea)
Several less common adverse reactions (<1%).For opioid-induced constipation:

Nausea: ~ 11%; 1% severe nausea and 2% discontinued treatment due to nausea. Diarrhea: ~ 8%; 2% severe diarrhea and 1% of patients discontinued treatment due to diarrhea. Less common adverse reactions (<1%): fecal incontinence, blood potassium decreased.For subjects with irritable bowel syndrome with constipation:

Nausea: ~ 8%; 1% severe nausea and 1% discontinued treatment due to nausea. Diarrhea: ~ 7%; <1% of patients had severe diarrhea and <1% of patients discontinued treatment due to diarrhea. Less common adverse reactions: <1%A 2018 pooled analysis from three phase III, randomized, double-blind, placebo-controlled studies on usage for Opioid-Induced Constipation, found that the numbers of patients reporting adverse effects were similar in both the lubiprostone and placebo treatment groups for all opioid classes (P ≥ 0.125); however, gastrointestinal adverse effects were reported more frequently by those receiving lubiprostone than 2 of the 3 opioid groups. The most commonly reported TEAEs in the lubiprostone treatment groups were nausea (13.4%–18.1%), diarrhea (1.2%–13.9%), and abdominal pain (4.7%–5.6%).
Medical uses
Lubiprostone is a laxative used for the treatment of constipation, specifically:
Chronic idiopathic constipation (difficult or infrequent passage of stools that lasts for 3 months or longer and is not caused by diet, disease, or drugs).Constipation caused by certain opioid (narcotic) pain medications in people with chronic (on-going), noncancer pain, or in patients with long-lasting pain caused by a previous cancer or its treatment who do not need weekly increases in opioid dosage.The effectiveness of lubiprostone has not been established in patients who are taking a diphenylheptane opioid (e.g., methadone).Irritable bowel syndrome with constipation (IBS-C; a condition that causes stomach pain or cramps, bloating, and infrequent or difficult passage of stools) in women who are at least 18 years of age.Lubiprostone has not been studied in children. There is current research under way to determine the safety and efficacy in postoperative bowel dysfunction. It comes in a liquid filled capsule and is available only with a doctors prescription. If one misses a dose it should be taken as soon as possible unless it is almost time for the next dose, in which case it should be skipped and the user should return to their regular dosing schedule. Adverse effects
In clinical trials, the most common adverse event was nausea (31%) . Other adverse events (≥5% of patients) included diarrhea (13%), headache (13%), abdominal distension (5%), abdominal pain (5%), flatulence (6%), sinusitis (5%), vomiting (5%), and fecal incontinence (1%).