Dr.AddMedPHL 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…

Worth saying plainly that not all of this is benign. Severe constipation on delayed gastric emptying has produced obstruction and ileus cases, rarely but genuinely. Pain with vomiting and no bowel movement is not a fiber conversation.

MounjBrad said:

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

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: taking a digestive enzyme supplement. 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.

Dr.SportsMedIN said:

Worth saying plainly that not all of this is benign.

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.

One thing that is still open after james_edin’s answer:

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

OP back with an update, since a thread like this is useless without one.

Water and magnesium first, soluble fiber second, and dropping the bran entirely. Resolved in about a week after two months of getting it backwards.