FDA clears Plenity, a hydrogel weight-management device

In April 2019, the Food and Drug Administration cleared Plenity, also known by its ingredient name Gelesis100, as a medical device for weight management rather than approving it as a drug ^[1][2]. The clearance covers adults with a body mass index of 25 to 40, used along with diet and exercise, and it does not require patients to have an obesity-related health condition ^[2][3].

Plenity works differently from appetite-suppressing drugs. Each capsule contains particles made from cellulose and citric acid. When swallowed with water before a meal, the particles absorb water in the stomach and form a hydrogel that takes up about a quarter of the stomach's volume, mimicking the texture of chewed food ^[1][2]. The gel is not absorbed into the bloodstream. It travels through the small intestine largely intact, breaks down partially in the large intestine, and the leftover cellulose passes out in stool ^[2].

The main evidence comes from the Gelesis Loss of Weight (GLOW) study, a 24-week, randomized, double-blind, placebo-controlled trial with 436 adults, 223 on Gelesis100 and 213 on placebo ^[2]. Average age was 48, and average BMI was 34 ^[2]. Mean weight loss was 6.4% in the treatment group versus 4.4% with placebo, a statistically significant difference ^[2]. Fifty-nine percent of people taking Plenity lost at least 5% of their body weight, compared with 42% on placebo, and the company reports that responders lost an average of about 10% of body weight, or roughly 22 pounds, along with about 3.5 inches off the waist ^[2][3]. Gelesis also describes a subgroup of "super responders," about 26% of participants, who lost an average of 14% of body weight, or about 30 pounds ^[3]. Among participants with prediabetes or untreated type 2 diabetes, mean weight loss reached 8.1% with Plenity versus 5.6% with placebo ^[2].

A 48-week extension study, GLOW-EX, followed 39 people who had lost at least 3% of body weight in the original trial. Those who stayed on Gelesis100 had 7.6% mean weight loss at 48 weeks, up from 7.1% at 24 weeks, while those switched from placebo to the device reached 9.4%, up from 7.1% ^[2]. The most common side effects in the main trial were gastrointestinal, such as diarrhea, bloating, infrequent bowel movements and gas, and these were somewhat more frequent in the treatment group, though overall adverse event rates were similar to placebo and mostly mild or moderate ^[1][2][3]. The device should not be used by people who are pregnant, are allergic to its ingredients, or have esophageal abnormalities, strictures, or a history of gastrointestinal surgery that altered motility ^[1][2][3].

Why it matters for patients

Plenity is not a GLP-1 medicine like semaglutide or tirzepatide. It is a device, not a drug, and it works by physically filling space in the stomach rather than acting on hormones or the brain ^[1][2]. That means it does not carry the systemic side effects associated with GLP-1 drugs, but the weight loss shown in trials, an average of 6.4% over 24 weeks, is smaller than what many people see with GLP-1 medications ^[2]. Its clearance for a BMI as low as 25, without requiring another health condition, opens it to some overweight adults who may not qualify for certain prescription drugs ^[2]. At the time of clearance, Gelesis said it would work to keep the product affordable out of pocket, though exact pricing was not yet public ^[1].

What happens next

At the time of the FDA clearance, Gelesis said a limited launch was expected in the second half of 2019, with wider U.S. availability planned for 2020 ^[1]. Pricing details had not been released as of the clearance announcement ^[1].