Trulance (plecanatide) works by mimicking a natural hormone in your gut that draws water into your intestines, softening stool and making it easier to pass. It’s approved for two conditions: chronic idiopathic constipation (CIC) and irritable bowel syndrome with constipation (IBS-C). Understanding the mechanism helps explain why it works differently from older laxatives and why its side effect profile is relatively mild.
The Hormone Trulance Copies
Your body naturally produces a hormone called uroguanylin in the lining of your small intestine. Uroguanylin’s job is to regulate fluid balance in your gut by activating a specific receptor called guanylate cyclase-C (GC-C) on the surface of intestinal cells. When that receptor gets switched on, it triggers a chain of events that pulls water into the intestinal space, keeping stool hydrated and moving.
Trulance is a synthetic version of uroguanylin, nearly identical in structure. The only difference is a single amino acid swap near one end of the molecule. This small change makes Trulance slightly more potent than the natural hormone while preserving one of its most important features: pH sensitivity. That means Trulance is most active in the mildly acidic environment of the upper small intestine, right where fluid regulation matters most.
What Happens Inside the Intestine
Once Trulance binds to GC-C receptors on the cells lining the intestinal wall, it sets off a specific signaling cascade. The receptor produces a messenger molecule called cGMP inside the cell. That messenger does two things simultaneously. First, it activates a chloride channel on the surface of the cell that faces the inside of the gut. This channel pumps chloride and bicarbonate ions out into the intestinal space. Second, cGMP reduces the activity of a sodium pump that normally absorbs sodium (and water along with it) back into the body.
The combined effect creates an ionic gradient, essentially a chemical pull that draws water from the body into the intestinal lumen. The result is more fluid surrounding the stool, which softens it and increases intestinal volume enough to trigger natural contractions that move things along. This is the same mechanism your body already uses to regulate intestinal hydration. Trulance just amplifies it.
The Built-In Safety Brake
One of Trulance’s more interesting design features is borrowed directly from uroguanylin: a self-regulating feedback loop. Because Trulance is most active in acidic conditions, and because its own activity causes bicarbonate secretion (which raises pH and makes the environment more alkaline), the drug gradually dials itself down as it works. Higher pH means less binding to the receptor, which means less fluid secretion.
This is a meaningful distinction from linaclotide (Linzess), the other major GC-C agonist on the market. Linaclotide was modeled after a bacterial toxin and activates the same receptor more potently, with less sensitivity to pH changes. It lacks that built-in off switch. This likely explains why diarrhea rates tend to be lower with Trulance. In clinical trials, diarrhea occurred in about 5% of Trulance-treated patients with CIC compared to 1% on placebo, and 4.3% of IBS-C patients compared to 1% on placebo. Severe diarrhea was uncommon, affecting roughly 0.6% to 1% of patients depending on the condition being treated.
How Well It Works in Practice
For chronic idiopathic constipation, clinical trials measured how many patients achieved at least three complete spontaneous bowel movements per week, sustained over most of a 12-week period. About 21% of patients taking Trulance hit that benchmark, compared to 11.3% on placebo. That gap may sound modest, but it’s worth remembering that the bar was set high: patients had to maintain the improvement for at least 9 out of 12 weeks.
For IBS-C, the trials used a tougher composite measure that required both a 30% or greater improvement in worst abdominal pain and at least one additional complete spontaneous bowel movement per week, in the same week, for at least 6 of 12 weeks. About 26% of patients on Trulance met that standard, compared to 16% on placebo. The pain component is notable because Trulance isn’t a painkiller. The reduction in abdominal pain likely comes from decreased intestinal distension as stool moves more normally, and possibly from cGMP’s effects on pain-sensing nerve fibers in the gut wall.
How to Take It
Trulance is a once-daily tablet that can be taken with or without food. For people who have difficulty swallowing, the tablet can be crushed and mixed into a teaspoon of room-temperature applesauce, then consumed immediately. It can also be dissolved in water. The crushed tablet hasn’t been tested in other soft foods or liquids, so applesauce and water are the recommended options.
Because the drug acts locally in the gut lining and is barely absorbed into the bloodstream, systemic side effects are rare. The vast majority of the drug stays in the intestinal tract and is broken down there. Diarrhea is the primary side effect to watch for, and if it becomes severe, stopping the medication resolves it.
Who Should Not Take Trulance
Trulance carries a boxed warning against use in children under 6 years old. In young children, the intestinal receptors that Trulance targets are more abundant and more active, which creates a risk of serious dehydration from excessive fluid secretion. The drug is also not recommended for children aged 6 through 17, as it hasn’t been adequately studied in that age group. It should not be used by anyone with a known or suspected mechanical bowel obstruction, since increasing fluid and motility in a blocked intestine can cause dangerous complications.