kevin_tulsa said:

The mechanism is slowed transit plus reduced intake, and that combination determines which interventions work.

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.

A narrower follow-up, since the general answer is now clear:

What the mechanism is, because if it is transit rather than water then fiber is the wrong lever?

PeptideChemSF said:

Gastric emptying studies and constipation: semaglutide delays gastric emptying by ~40% at steady state, as measured by acetaminophen absorption…

Sulfur burps on constipation — the most underrated side effect nobody warned me about. 🤢 The smell is absolutely vile and comes on without warning.

What finally helped: eliminating eggs and cruciferous vegetables. Also, eating smaller portions and chewing thoroughly reduces the gas production.

If sulfur burps persist beyond 2-3 weeks, talk to your provider — it could indicate gastroparesis that needs medical attention.

Reporting back.

Update — the osmotic agent was the thing. I had been reaching for a stimulant, which was making the next day worse.

carl_compliance said:

Sulfur burps on constipation — the most underrated side effect nobody warned me about.

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.