PedsEndoPhilly said:

The escalation order that reflects the mechanism: water and salt first, then soluble fiber, then magnesium or an osmotic agent, then a stimulant only…

Saving this. It is the first explanation that did not require me to already understand it. Sending this to two other people who asked me the same thing last week.

Adding the clinical framing, because it changes how the question reads.

Gastric emptying studies and constipation: semaglutide delays gastric emptying by ~40% at steady state, as measured by acetaminophen absorption testing and scintigraphy[1].

Clinically relevant implications:

• Explains early satiety and nausea
• Affects absorption of co-administered oral medications
• Creates aspiration risk for procedures under anesthesia
• Contributes to constipation via slowed GI transit

Importantly, the gastric emptying delay attenuates with continued use (tachyphylaxis), which correlates with the transient nature of GI side effects.

lisa_labSD said:

Acid reflux and constipation: I developed GERD symptoms around week 4 that I'd never had before.

Drug interaction alert relevant to constipation: if you take oral levothyroxine (Synthroid), GLP-1 agonists can reduce absorption due to delayed gastric emptying. My TSH drifted up after starting semaglutide.

Solution: take levothyroxine on an empty stomach, 60 minutes before any food, and have your TSH rechecked 6-8 weeks after starting or changing GLP-1 dose. My endo had to increase my Synthroid by 12.5mcg.

Dr.GastroMayo said:

I added fiber, made it noticeably worse, and only later worked out that I had added the bulk without adding the water.

Heartburn management on constipation: Gaviscon before bed has been my savior. The delayed gastric emptying means stomach acid just sits there.

Don't ignore persistent heartburn — chronic acid exposure can damage your esophagus. If OTC remedies aren't cutting it after 2 weeks, see your doctor for something stronger. You shouldn't suffer through this.

Moderator note: a post naming a supplier has been edited. Discuss suppliers in the review sections, not here. Tagging this one for the weekly digest.