The highest FDA-approved dose of Linzess (linaclotide) is 290 mcg, taken once daily by mouth. This dose is specifically approved for adults with irritable bowel syndrome with constipation (IBS-C). Lower doses of 145 mcg and 72 mcg are used for other conditions and age groups.
Available Doses and What They Treat
Linzess comes in three capsule strengths: 72 mcg, 145 mcg, and 290 mcg. Which one you’re prescribed depends on your diagnosis and age.
For adults with IBS-C, the recommended dose is 290 mcg once daily. For adults with chronic idiopathic constipation (CIC), the starting dose is 145 mcg once daily, though it can be reduced to 72 mcg based on how you respond or how well you tolerate it. There is no approved dose higher than 290 mcg for any condition.
Children and teenagers have lower recommended doses. For patients aged 7 to 17 with IBS-C, the dose is 145 mcg once daily. For children aged 6 to 17 with functional constipation, the dose is 72 mcg once daily. The pediatric functional constipation approval came in June 2023, making Linzess the first medication approved for that use in children.
Why 290 mcg Is Only for IBS-C
Linzess works by activating receptors on the cells lining your intestines. When those receptors are triggered, the cells release more fluid into the intestinal space, which softens stool and speeds up movement through the gut. The same process also produces a signaling molecule that calms pain-sensing nerves in the colon wall. This is why the higher 290 mcg dose is reserved for IBS-C: it’s a condition that involves both constipation and abdominal pain, so the stronger dose addresses both problems more aggressively.
Chronic constipation without the pain component of IBS typically responds to the 145 mcg or 72 mcg dose, so the added intensity of 290 mcg isn’t necessary and would only increase the chance of side effects.
Diarrhea Risk Increases With Dose
Diarrhea is the most common side effect at every dose level, and it tracks closely with dose strength. In clinical trials, about 20% of adults taking the 290 mcg dose for IBS-C experienced diarrhea, compared to 16% of adults on the 145 mcg dose for chronic constipation. In a separate trial that directly compared the two lower doses, 19% of patients on 72 mcg and 22% on 145 mcg reported diarrhea, versus 7% on placebo.
This is why prescribers sometimes start CIC patients at 72 mcg rather than 145 mcg, particularly if you have a history of loose stools or are concerned about tolerability. The medication works through fluid secretion, so diarrhea is essentially an exaggerated version of its intended effect.
How to Take It for Best Results
Regardless of dose, Linzess should be taken on an empty stomach at least 30 minutes before your first meal of the day, at roughly the same time each morning. This timing matters. Taking it right after a high-fat meal has been shown to cause looser stools and more frequent bowel movements than taking it in a fasted state. In other words, food doesn’t block the drug from working, but it changes how intensely it hits your gut, often in an unpleasant way.
No dose adjustments are needed for people with kidney or liver problems. The drug acts locally in the intestine and has minimal absorption into the bloodstream, so organ function elsewhere in the body doesn’t significantly change how it behaves.
What Happens at Doses Above 290 mcg
There is no approved dose above 290 mcg, and taking more than prescribed increases the risk of severe diarrhea, dehydration, and electrolyte imbalances. Animal studies conducted during the drug’s development found that very high doses caused significant fluid loss, reduced activity, and in extreme cases at doses hundreds of times above the human range, tremors and convulsions. These effects were all tied to the same fluid-secretion mechanism that makes the drug work at normal doses.
Linzess also carries a boxed warning against use in children under 2 years old. In very young mice, high doses caused fatal dehydration because their intestines lacked the capacity to reabsorb the excess fluid. This risk doesn’t apply to older children or adults at approved doses, but it underscores why sticking to the prescribed strength matters.