Phentermine and Constipation

Phentermine and Constipation

Constipation is one of the most common side effects of phentermine. In addition to the day-to-day discomfort and pain, ongoing phentermine constipation can also slow weight loss.

Medically, constipation is evidenced by either infrequent or difficult-to-pass stools. Changes in routine, increased stress, some medications, and certain medical conditions can all cause constipation ( 1 ).

Thankfully, most cases of phentermine constipation resolve within a few days, without medical intervention.

Does Phentermine Cause Constipation?

woman with phentermine constipation
Nearly half of phentermine patients experience phentermine constipation

Yes, phentermine causes constipation in many users. In fact, it is the third most common side effect of this medication, and almost 50% of users report phentermine constipation ( 2 ).


Avoid the Discomfort. Lose Weight.

Phen Caps is recommended by over 30,000 people like you who want to lose weight fast and effectively without the drawbacks of phentermine.

  • No Prescription Required.
  • No Side Effects.
  • Made in USA.

So, when is it considered constipation?

Many people think that it’s necessary to have a certain number of bowel movements per day or week, but the truth is that everyone is different. As long you feel healthy and regular, it’s perfectly fine to go a few days without a bowel movement.

However, fewer than three bowel movements a week is considered constipation ( 1 , 3 ).

As well as problems passing stools, phentermine constipation can also cause swollen abdomen, bloating, stomach pain, nausea, vomiting, and temporary weight gain.

Duromine and Constipation

Duromine is a popular brand of phentermine weight loss pills in Australia, New Zealand, and South Africa.

Like other brands of phentermine, these capsules commonly cause constipation. Phentermine resin is a stimulant, which – in combination with dietary changes and potential stress –increases patients’ risk of Duromine constipation.


Buy Phen Now!

  • No Prescription Required.
  • No Side Effects.
  • Made in USA.
Get 20% off now!

If your bowel movements are irregular, infrequent, or hard to pass for more than a couple of days while taking Duromine, contact your prescribing doctor.

Why Does Phentermine Cause Constipation?

Phentermine causes constipation because the main ingredient acts as a stimulant and because many patients dramatically change their diet and exercise routines to maximize their weight loss.

CNS Stimulation

Drink enough water
Exercise and hydration often function as at-home phentermine constipation remedies

Phentermine stimulates the central nervous system. This causes a release of neurotransmitters that increase energy and suppress appetite. Unfortunately, these same chemicals can also cause unwanted side effects like phentermine constipation.

As part of the “fight or flight” response that produces a reduction in appetite, the brain also signals the body to divert resources away from active digestion, which slows peristalsis: muscle contractions that move food through the digestive tract ( 4 ). When digestion is slowed for too long, it can cause constipation. This is why many phentermine users complain of problems passing stool.

Inadequate fluid intake may also contribute to phentermine constipation, in addition to exacerbating dry mouth and headaches. Stimulants can cause dehydration, and if there is not enough water in the body available to help expel waste products through stools, which are typically 75% water, it may cause constipation ( 5 , 6 ).

Dietary & Emotional Changes

stressed woman with phentermine constipation
Stress can affect bowel movements and may worsen phentermine constipation

Constipation can also be a result of changes in routine, stress, depression, or anxiety.

This medication is a strong appetite suppressant, so people eat tend to eat significantly less while taking it. Decreased food intake can slow digestion and produce this uncomfortable side effect ( 7 ).

Phentermine constipation is especially common in patients whose diets limit the intake of certain food groups. For example, low-carb diets (like carnivore and keto) pose a particular threat given followers’ tendency to dramatically decrease the intake of fiber-rich foods like whole grains and produce.


Get your FREE Phentermine Guide!

Learn more about popular brands, dosage, side effects, results, and weight loss alternatives.

Get my eBook

Stress, depression, and anxiety can also cause or worsen constipation ( 3 ). Major weight loss is inherently stressful, and phentermine can cause depression, anxiety, and other mood changes. As a result, for many users, emotional distress may also contribute to phentermine constipation.

How to Relieve Constipation Due to Phentermine

Going a day or two without a bowel movement might have you reaching for the laxatives, but consider a natural phentermine constipation remedy before you run to the drug store. Many behaviors that naturally help relieve phentermine constipation boost weight loss as well.

Here are five practical and effective phentermine constipation remedies:

1. Drink More Water

The easiest phentermine constipation remedy is to increase fluid intake.

Your organs need water to function properly, and the digestive system is no exception. When there is not enough water, the body pulls fluid from stool, which can make feces dry and hard to pass. To minimize dehydration, try to drink at least eight glasses (two liters) of water or other calorie-free, caffeine-free beverages each day. Avoid dehydrating drinks such as coffee, colas, energy drinks, and alcohol.

If you’re already drinking plenty of water, try adding a glass of warm water with lemon in the morning. Warm water increases the tightening of the intestines, which then facilitates bowel movements. The lemon helps as its high acid content stimulates the digestive system to get things moving ( 8 ).

broccoli, which contains fiber to relieve phentermine constipation
Eating more fiber-rich foods, like broccoli, can help relieve phentermine constipation

2. Focus on Fiber

There are two types of dietary fiber, and both help to treat and prevent constipation. Soluble fiber helps decrease cholesterol levels and makes stools easier to pass, while insoluble fiber helps promotes regular bowel movements ( 9 ).

Adult women need 25 grams of fiber per day, while men require 38 grams on average ( 10 ).

To fight phentermine constipation, eat more fiber-rich foods like whole fruit and vegetables with edible skins, whole grains, and legumes (e.g., lentils, beans, or peas).

NOTE: Eating more fiber can worsen constipation if you’re not getting enough fluids. So, as you increase fiber intake, make sure to drink plenty of water as well.

3. Get Moving

Regular physical activity increases blood flow to the intestines and promotes keeping your abdominal muscles in shape. Both help keep stool moving.

So, make exercise a part of your daily routine. Aerobic exercises like walking, running, swimming, or cycling provides the most benefit, but even a little gentle stretching or yoga can help ( 11 ).


0% Constipation. 100% Weight Loss.

Phen Caps is recommended by over 30,000 people like you who want to lose weight fast and effectively without the drawbacks of phentermine.

  • No Prescription Required.
  • No Side Effects.
  • Made in USA.

4. Manage Stress

Stress, depression, and anxiety worsen constipation, and phentermine is known to exacerbate these negative emotions, so effective stress management is critical for both weight loss and phentermine constipation relief.

Reduce stress with yoga, meditation, deep breathing, doodling, reading a book, or talking to a friend.

5. Try Prunes

No, it’s not just an old wives’ tale: prunes really do provide powerful relief for constipation. Prunes, or dried plums, are rich in insoluble fiber and contain sorbitol, which acts as a natural laxative.

In a 2018 study, subjects experienced significant increases in both stool frequency and stool weight after consuming 80-120 grams of prunes per day ( 12 ). That’s about 10-14 prunes each day.

Can I Take a Laxative with Phentermine?

Ask a pharmacist before combining phentermine with Miralax or any other laxative

ALWAYS check with your doctor and pharmacist before taking any additional medications or supplements alongside phentermine.

Some people take a laxative with phentermine to help relieve mild, short-term constipation. However, these medications are not safe for everyone, and they act quickly, so do not use laxatives and phentermine together without talking to your doctor & pharmacist first.

Do NOT take stool softeners or laxatives for more than two weeks at a time. Consult a doctor if phentermine constipation interferes with your daily activities, worsens, or does not go away.

Back to All Phentermine Side Effects

  1. Mayo Clinic Staff. (2018, January 10). Constipation.
  2. Members of “Losing Weight with Phentermine” Support Group on Facebook & Forum. (2019, March 13). [User Report of Common Phentermine Side Effects]. Unpublished raw data
  3. National Health Service. (2017, December 20). Constipation.
  4. Silverthorn, D. U. (2009). Human physiology: An integrated approach (4th ed.). Harlow: Pearson Education.
  5. Martin, E. B., Jr., & Hammerness, P. G. (2014, August). Thirsty: ADHD, Stimulant Medication, and Dehydration. Attention, 26-27.
  6. The Editors of Encyclopaedia Britannica. (2002, June 14). Feces. In Encyclopaedia Britannica.
  7. Towers, A. L., Burgio, K. L., Locher, J. L., Merkel, I. S., Safaeian, M., & Wald, A. (1994). Constipation in the elderly: Influence of dietary, psychological, and physiological factors. Journal of the American Geriatrics Society, 42(7), 701-706. doi:10.1111/j.1532-5415.1994.tb06527
  8. Baucom, M. (2017, April 3). Do This and That: Taking Proven Chronic Constipation Remedies to the Next Level (E. K. Luo MD, Ed.).
  9. UCSF Medical Center. (n.d.). Increasing Fiber Intake.
  10. Dahl, W. J., & Stewart, M. L. (2015). Position of the Academy of Nutrition and Dietetics: Health Implications of Dietary Fiber. Journal of the Academy of Nutrition and Dietetics, 115(11), 1861-1870. doi:10.1016/j.jand.2015.09.003
  11. Smith, M. W. (Ed.). (2018, June 25). Exercise for Constipation Relief: Which Exercises to Do.
  12. Lever, E., Scott, S. M., Louis, P., Emery, P. W., & Whelan, K. (2018). The effect of prunes on stool output, gut transit time and gastrointestinal microbiota: A randomised controlled trial. Clinical Nutrition. doi:10.1016/j.clnu.2018.01.003