Constipation on GLP-1: pathophysiology and fiber protocol — November 2025

Constipation is a very common side effect — reported in 10-24% of participants in SURMOUNT trials depending on dose. It's a direct consequence of delayed gastric and intestinal transit.

5 days is uncomfortable but not immediately dangerous in most cases. However, I'd want to rule out a few things:

• Any severe abdominal pain (not just bloating)?
• Any vomiting?
• Any fever?

If yes to any of those, get evaluated today. If it's just bloating and discomfort:

1. Miralax (PEG 3350): increase to a full dose (17g) daily. Give it 48-72h to work — it's an osmotic laxative, not a stimulant, so it takes time.
2. Add a stimulant laxative like bisacodyl (Dulcolax) or senna if Miralax alone isn't cutting it.
3. Magnesium citrate (the liquid bottle, not capsules) is the nuclear option and will almost certainly work, but stay near a bathroom.
4. Hydration — you need to be drinking significantly more water on GLP-1s. Aim for 80-100 oz/day minimum.

Long-term management: daily fiber supplement (psyllium husk), adequate water, and if constipation persists, discuss prescription options like linaclotide with your provider.

Oh god I remember this phase. I went 7 days once in month 2 and nearly lost my mind. Here's what eventually became my routine:

• Morning: large glass of warm water with lemon, 2 tbsp ground flaxseed mixed in
• Daily: Miralax in my afternoon water
• Nightly: 400 mg magnesium glycinate (gentler than citrate, won't give you the runs)
• Prunes. I know. I'm 34 and eating prunes like a grandma. They work.

It took about 8 weeks on tirz for my gut to recalibrate, and now I go every 1-2 days which for me on this drug, I'll take it.

Can I just say — nobody warns you about this adequately. My doctor was like "you might get some constipation" like it's a minor inconvenience. NO. It's sitting on the toilet for 30 minutes passing what feels like a boulder. It's the bloating making you look 6 months pregnant. It's the anxiety of "is something actually wrong inside me."

What finally helped me: Smooth Move tea (senna-based herbal tea) every other night. Not every night because you can become dependent on stimulant laxatives. And walking — 30 min walks genuinely help motility.

UPDATE: magnesium citrate worked. I'll spare you all the details but let's just say it WORKED. Aggressively. 💀

Going to start the daily Miralax + magnesium glycinate routine going forward. Thank you all for the advice and for making me feel less alone in this extremely unglamorous side effect.