Does Phentermine cause constipation?
Bottom line
Yes. Constipation is listed among the common adverse reactions on Phentermine's own FDA label, published 2026-06-15.
No clinician has reviewed this page. Label and trial statements are quoted from the FDA label or the trial cited beside them. General guidance is marked as such, and every price carries the date it was verified. That is sourcing, not medical review. What we do and do not check · Who checked the price
Last updated 2026-06-15 — the FDA label this page quotes. Read and dated by Alex Seot.
Does Phentermine cause constipation?
Yes, and it is on the label rather than only in reports: constipation appears among the common adverse reactions in Phentermine's FDA prescribing information, published 2026-06-15. This label names its reactions without incidence rates, so it says the reaction occurs, not how often. Phentermine is not a GLP-1 and does not slow gut transit the way those drugs do; its label lists constipation among the common reactions without naming a mechanism. Eating much less compounds it on any weight-loss drug: less food means less fiber and less fluid, and both are what keep things moving. Phentermine starts at 37.5 mg once daily, in the morning with no dose escalation, so there are no step-ups for it to cluster around. What helps first: fluid first. It is the most common deficit and the easiest to fix. It stops being ordinary at a specific line: no bowel movement for several days with abdominal pain, distension or vomiting. That combination needs assessment rather than another laxative.
What helps with constipation on Phentermine?
- 1Fluid first. It is the most common deficit and the easiest to fix.
- 2Fiber added gradually rather than all at once, which otherwise trades constipation for bloating.
- 3Movement, which does more for gut transit than most supplements.
- 4Asking the prescriber about a stool softener or an osmotic laxative before reaching for a stimulant one.
The label approves it as a short-term adjunct, a few weeks. Every monthly subscription selling it as ongoing therapy is using it beyond that duration, and the withdrawal the label describes is what makes leaving one harder than joining it.
When is constipation on Phentermine serious?
No bowel movement for several days with abdominal pain, distension or vomiting. That combination needs assessment rather than another laxative.
Other reactions on Phentermine's label with a page of their own
Would switching drugs help?
Constipation is on 12 of the 13 FDA labels tracked here, so the other labels are worth reading before assuming a switch avoids it. What a switch does change is what you pay.
Every alternative to Phentermine, with each one's verified price and the date it was read →
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The listing, the schedule and the warnings are read from FDA prescribing information for phentermine hydrochloride tablets (Aurolife Pharma), published 2026-06-15; the notes on why it happens and what helps are general guidance, not label text. Information only, not medical advice — a symptom that worries you is a call to your prescriber, not a search result.