By William Elliott, MD, FACP, and James Chan, PharmD, PhD

Dr. Elliott is Assistant Clinical Professor of Medicine, University of California, San Francisco.
Dr. Chan is Associate Clinical Professor, School of Pharmacy, University of California, San Francisco.

Drs. Elliott and Chan report no financial relationships relevant to this field of study.

The FDA has approved hydrogel capsules for weight management. The capsules contain nonsystemic, superabsorbent hydrogel particles formed from cellulose and citric acid.1 These particles are hydrated after ingestion to 100 times their original weight, creating a sensation of fullness in the stomach and small intestine before break down in the colon and elimination through normal bowel movement.1 This product is cleared as a prescription device rather than a drug, meaning it does not achieve its primary intended use through chemical action within or on the body.2 Hydrogel capsules will be marketed as Plenity.


Used in conjunction with exercise and proper diet, hydrogel capsules should be used for weight management in overweight and obese adults with a body mass index (BMI) 25 kg/m2 to 40 kg/m2.1


The recommended dose is three capsules taken twice a day, 20 to 30 minutes before lunch and 20 to 30 minutes before dinner.1 The capsules should be taken with water and followed with two additional glasses (8 oz) of water. Plenity is available as 0.75 g per capsule.


Hydrogel capsules provide a nonsystemic alternative as an aid to weight management.


Hydrogel should be used with caution in patients with gastroesophageal reflux disease, ulcers, or heartburn.1 Avoid prescribing the capsules for patients with esophageal anatomic anomalies (e.g., diverticuli), for patients with suspected strictures (e.g., Crohn’s disease), and for patients who have undergone prior gastrointestinal (GI) surgery that could affect GI transit.


The safety and effectiveness of hydrogel capsules were evaluated in a randomized, double-blind, placebo-controlled study.1,3 Subjects ranged in age from 22 to 65 years (mean, 48 years), mean BMI was 34 kg/m2, and fasting blood glucose levels were ≥ 90 mg/dL but ≤ 145 mg/dL. Those with BMI < 30 kg/m2 needed to present with at least one of the following comorbidities: dyslipidemia, hypertension, or drug-naïve or metformin-treated type 2 diabetes. Subjects were randomized to hydrogel (n = 223) or placebo (n = 213). The primary effectiveness endpoint was change in body weight from baseline at day 171 and the proportion of subjects who lost ≥ 5% of body weight. The mean changes in weight were -6.4% (from baseline of 215 pounds) for hydrogel capsules compared to -4.4% for placebo (baseline of 222 pounds), a between-group difference of -2.1% ± 0.6%, showing statistical superiority over placebo. Fifty-nine percent of subjects on hydrogel capsules achieved ≥ 5% weight loss compared to 42% of subjects on placebo. Forty percent of subjects achieved weight loss of ≥ 7.5% and 27% ≥ 10% with hydrogel capsules compared to 24.5% and 16% of subjects, respectively, on placebo. For responders (≥ 5%), the mean weight loss was 10.2% (± 4.1%). Early response was a predictor of response, as more than 85% who ultimately achieved ≥ 5% weight loss lost ≥ 3% at eight weeks. Hydrogel capsules were particularly effective in subjects with prediabetes or drug-naïve type 2 diabetes, as 53% achieved ≥ 7.5% weight loss compared to 25% for placebo. Subjects who lost ≥ 3% body weight in the previously mentioned double-blind study were enrolled in an open-label extension study.3 Those originally on placebo were crossed over to hydrogel capsules (n = 18), and those originally on hydrogel capsules continued on those capsules (n = 21). Continued treatment with hydrogel capsules showed an additional 0.8% ± 3% weight loss after an additional 24 weeks of treatment. Those who crossed over from placebo lost an additional 3% ± 4%. Overall, GI-related adverse reactions (e.g., abdominal distention, diarrhea, abdominal pain) were greater with hydrogel capsules. Generally, these adverse reactions were mild and occurred within three months. There were no significant differences in cardiovascular risk factors between groups (e.g., plasma lipids, blood pressure, or surrogate for insulin resistance [homeostatic model assessment of insulin resistance]).3 Hydrogel capsules do not appear to affect absorption of various vitamins (e.g., A, B1, B2, B12, B6, B9, D, E).


Obesity is a common disorder, with a prevalence of 39.8% among adults in the United States in 2015-2016.4 Lifestyle modification is the recommended initial therapy; weight loss medication is initiated as an adjunct therapy.5 The American Association of Clinical Endocrinologists and the American College of Endocrinology list the following FDA-approved weight loss medications for long-term treatment of obesity: orlistat, lorcaserin, phentermine/topiramate, naltrexone/bupropion, and liraglutide. All these are absorbed systemically and carry the potential for adverse reactions and safety concerns. Hydrogel capsules offer a potential novel, nonsystemic option that appear to be effective with minimal adverse reactions. The product is expected to be available in the second quarter of 2019. Cost was not available at the time of this review.


  1. Gelesis, Inc. Plenity Instructions for Use, April 2019. Available at: Accessed May 7, 2019.
  2. U.S. Food & Drug Administration. Is the Product a Medical Device? Updated March 22, 2018. Available at: Accessed May 7, 2019.
  3. Greenway FL, Aronne LJ, Raben A, et al. A randomized, double-blind, placebo-controlled study of Gelesis100: A novel nonsystemic oral hydrogel for weight loss. Obesity 2019;27:205-216.
  4. U.S. Department of Health and Human Services. Prevalence of Obesity Among Adults and Youth: United States, 2015-2016. Published October 2017. Available at: Accessed May 7, 2019.
  5. The American Association of Clinical Endocrinologists and The American College of Endocrinology. AACE/ACE Algorithm for the Medical Care of Patients With Obesity, 2016. Available at: Accessed May 7, 2019.