Linzess Side Effects: What to Expect and When to Call Your Doctor

Linzess (linaclotide) is an effective treatment for IBS with constipation (IBS-C) and chronic idiopathic constipation (CIC), but like all medications, it comes with potential side effects. Knowing what to expect—and when a side effect requires medical attention—can help you use Linzess safely and effectively. Here's everything you need to know about Linzess side effects in 2026.

The Most Common Side Effect: Diarrhea

Diarrhea is by far the most common side effect of Linzess. In clinical trials, up to 20% of adult patients reported diarrhea, depending on the dose and condition being treated. This happens because Linzess works by increasing fluid secretion into the intestine—the same mechanism that relieves constipation can cause loose, watery stools in some patients.

Key facts about diarrhea with Linzess:

• It often starts within the first 2 weeks of treatment
• Higher doses (290 mcg for IBS-C) cause diarrhea more frequently than lower doses (72 mcg, 145 mcg)
• Severe diarrhea was reported in 2% of adult patients with IBS-C or CIC treated with the 145 mcg or 290 mcg doses
• Diarrhea is also the most common reason patients discontinue Linzess

Common Side Effects of Linzess

The following side effects affect 1% or more of patients and are most commonly reported in clinical trials:

• Diarrhea: Mild to moderate in most patients; may be more frequent with higher doses
• Abdominal pain: Lower and upper abdominal cramping or discomfort
• Flatulence (gas): Increased gas is common, especially early in treatment
• Headache: May be related to fluid loss from diarrhea; staying well-hydrated can help
• Abdominal distension (bloating): Feeling of fullness or swelling in the abdomen
• Viral gastroenteritis: Stomach flu-like symptoms were reported in a small percentage of patients in trials

Less Common Side Effects

These side effects occur in fewer than 1% of patients but have been reported:

• Nausea and vomiting
• Gastroesophageal reflux disease (GERD)
• Fecal incontinence (loss of bowel control)
• Defecation urgency (sudden, strong urge to go)
• Hemorrhoidal hemorrhage, rectal hemorrhage, or hematochezia (blood in stool)

Serious Side Effects: When to Stop Linzess and Call Your Doctor

The following situations require you to stop taking Linzess and contact your healthcare provider immediately:

• Severe diarrhea: Post-marketing reports show severe diarrhea associated with dizziness, fainting (syncope), low blood pressure (hypotension), and electrolyte abnormalities (low potassium or sodium) requiring hospitalization or IV fluids
• Signs of a serious allergic reaction: Hives, difficulty breathing, swelling of the face, lips, tongue, or throat (anaphylaxis or angioedema)—seek emergency care immediately
• Black, bloody, or tarry stools: May indicate GI bleeding; stop Linzess and contact your doctor

Critical Warning: Keep Linzess Away from Children Under 2

Linzess carries a black-box warning: it is contraindicated in patients under 2 years of age. In animal studies, a single adult dose given to newborn mice caused death from severe dehydration within 24 hours. Keep Linzess stored in a childproof location, and seek emergency medical help immediately if a young child swallows any capsules.

Tips for Managing Common Linzess Side Effects

• Diarrhea: Stay well-hydrated. If severe, stop taking Linzess and call your doctor. Your provider may lower your dose (e.g., from 290 mcg to 145 mcg for IBS-C).
• Gas and bloating: Gentle exercise and movement can help relieve gas. Avoid gas-producing foods.
• Headache: May be related to dehydration from diarrhea. Drink plenty of fluids. Over-the-counter pain relievers such as acetaminophen may help—check with your pharmacist first.

When to Call Your Doctor

Call your doctor if you have severe or ongoing diarrhea, blood in your stool, dizziness or fainting, symptoms of an allergic reaction, or if your constipation symptoms are not improving after 2–4 weeks. Also review our guide on Linzess drug interactions to ensure there are no conflicts with your other medications.