In the population overall, the greatest likelihood of experiencing the first episode of any of these three TEAEs was greatest in the first week of treatment and decreased thereafter.According to Medscape, the most common (>10%) were: Nausea , Diarrhea (7-12%), Headache (2-11%). Less common side effects (1-10%) included: Abdominal pain (4-8%), Abdominal distension (3-6%), Flatulence (4-6%), Vomiting (3%), Loose stools (3%), Edema (1-3%), Abdominal discomfort (1-3%), Dizziness (3%), Chest discomfort/pain (2%), Dyspnea (2%), Dyspepsia (2%), Fatigue (2%), Dry mouth (1%). Contraindications
Known or suspected mechanical GI obstruction. Known hypersensitivity to lubiprostone or any ingredient in the formulation.There is no current data on use in people with liver or kidney complications. The effects on pregnancy have not been studied in humans but testing in guinea pigs resulted in fetal loss. Amitiza is not approved for use in children. Lubiprostone is contraindicated in patients exhibiting chronic diarrhea, bowel obstruction, or diarrhea-predominant irritable bowel syndrome. Mechanism of action
Lubiprostone is a bicyclic fatty acid derived from prostaglandin E1 that acts by specifically activating ClC-2 chloride channels on the apical aspect of gastrointestinal epithelial cells, producing a chloride-rich fluid secretion. These secretions soften the stool, increase motility, and promote spontaneous bowel movements (SBM). Symptoms of constipation such as pain and bloating are usually improved within one week, and SBM may occur within one day. Pharmacokinetics
Unlike many laxative products, lubiprostone does not show signs of drug tolerance, chemical dependency, or altered serum electrolyte concentration.
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%).