GLP-1 receptor agonists are widely used today for their effects on appetite and body weight control. One of the main mechanisms of action of this class of drugs is the delay of gastric emptying , meaning that the ingested contents remain longer in the stomach before passing into the small intestine. This effect, while desirable for increasing satiety, can have important implications for hydration.
Gastric emptying is a crucial step in fluid absorption. The water we ingest is not significantly absorbed in the stomach; it needs to reach the small intestine to be absorbed and effectively contribute to the body's fluid balance. When this transit is slower, the water remains in the stomach longer, which can delay its systemic absorption.
A recent meta-analysis, which compiled data from several clinical studies, demonstrated that the use of GLP-1 agonists is associated with an average delay of approximately 36 minutes in gastric emptying when compared to placebo, especially for solid contents, as measured by techniques such as scintigraphy. Although this delay may seem small, it becomes relevant in the context of daily life, particularly when associated with already reduced fluid intake.
In addition to delayed absorption, slower gastric emptying contributes to a prolonged feeling of gastric fullness . Many people using GLP-1 report feeling "full" with small volumes, which can spontaneously reduce the urge to drink water throughout the day. As a result, total fluid intake tends to decrease, even without a clear perception of thirst or dehydration.
This scenario creates an unfavorable combination: on the one hand, ingested water takes longer to be absorbed; on the other hand, total fluid intake may decrease. In situations of higher fluid demand, such as physical activity, exposure to heat, or insufficient electrolyte intake, this effect can become even more significant, intensifying the risk of dehydration.
Therefore, although GLP-1 agonists do not directly cause dehydration, the delayed gastric emptying documented in the scientific literature helps explain why some people may experience signs of inadequate hydration while using these medications. Attention to regular fluid intake throughout the day and adequate electrolyte intake becomes essential to minimize this physiological effect and maintain proper fluid balance.
