Most phentermine patients complain of constipation and trouble going while taking this weight loss medication, but some users have the opposite problem. Phentermine diarrhea can emerge as one of the earliest phentermine side effects and is often accompanied by nausea/vomiting, lightheadedness and other side effects.
Call a doctor right away if you have experience diarrhea while taking phentermine and an antidepressant together. This uncomfortable reaction is a listed side effect and can prove serious if it does not resolve quickly [1,2].
Yes, a small percentage of patients experience phentermine diarrhea. Less common side effects like loose stools and vomiting may occur when the stimulation from phentermine wears off and the body overcompensates while readjusting.
As a stimulant, phentermine produces a biological response similar to "fight or flight" that boosts energy and suppresses appetite.
However, if the body has been in this heightened state for too long, or as the stimulant wears off, the "rest and relax" system regains control and blood flows regularly to digestive system and muscles depending on demand . Unfortunately, sometimes when blood flow suddenly returns to the vessels surrounding the digestive tract, it can cause phentermine diarrhea.
While diarrhea is a known side effect of stimulants, based on patient accounts from the Facebook support group, this unpleasant side effect only lasts for a couple of days in most cases.
If you experience diarrhea while taking phentermine, talk to your doctor about possible solutions. He or she may recommend decreasing or splitting your dose, or even stopping the medication if your reaction is severe. Only a medical professional can determine the best course of action in your specific case.
Diarrhea, along with rapid heartbeat (tachycardia), shivering, sweating (diaphoresis), muscle cramps, agitation and elevated body temperature, are early symptoms of serotonin syndrome.
This condition occurs when you have too much serotonin – a vital neurotransmitter – circulating outside of cells. If left untreated, serotonin syndrome can lead to hypertensive/hyperthermic crisis and even death.
Patients who combine stimulants and antidepressants are at an increased risk of serotonin syndrome due to the two drugs’ effects on the body. Stimulants increase serotonin release and blood pressure, while antidepressants inhibit reuptake. The combination of the two medications can lead to dangerously high levels of the neurotransmitter .
Mild or passing phentermine diarrhea may be manageable at home, but talk to your doctor or seek medical attention if you have diarrhea while taking phentermine and it is interfering with your daily life or not going away.
Consider the following at-home remedies for phentermine diarrhea:
If you are struggling with phentermine diarrhea, steer clear of problematic foods and drinks that can make symptoms worse. High-fat or high-fiber foods, dairy and heavily-spiced dishes can aggravate diarrhea. Beverages that contain caffeine or alcohol have an equally unwelcome effect .
Re-hydrate with clear liquids, and then experiment with bland, low-residue foods like crackers, rice, toast, scrambled eggs or plain chicken to stay nourished throughout your bout of phentermine diarrhea.
Dehydration is a major concern if you have diarrhea, especially if you are losing a lot of fluid with each bowel movement. Make sure to drink plenty of water, broth and 100% fruit juice to replace lost fluids. Water is a good source of hydration, while the broth and juice serve to replace lost electrolytes .
If you cannot tolerate liquids by mouth for more than a day, or begin showing signs of dehydration, contact your doctor or go to an urgent care clinic. You may need intravenous fluids to stay hydrated.
Call your doctor or go the hospital if your diarrhea is severe, accompanied by other symptoms or lasts more than two days.
Acute dehydration and related electrolyte imbalances are one of the main concerns with ongoing diarrhea. Dehydration may be evidenced by symptoms such as lightheadedness, dry mouth, weakness or dark urine.
Go to the doctor if you display symptoms of dehydration from diarrhea. It is also critical to seek immediate medical attention if, at any point, your phentermine diarrhea is accompanied by severe abdominal/rectal pain, black/bloody stools or a fever higher than 102° F (39° C). These may be symptoms of a more serious problem .
Learn more about phentermine!
1. National Institutes of Health. (2017, May 15). Phentermine: MedlinePlus Drug Information.
2. Mayo Clinic Staff. (2018, January 11). Diarrhea: When to see a doctor.
3. Browning, K. N., & Travagli, R. A. (2014). Central Nervous System Control of Gastrointestinal Motility and Secretion and Modulation of Gastrointestinal Functions. Comprehensive Physiology, 1339-1368. doi:10.1002/cphy.c130055
5. Mayo Clinic Staff. (2016, October 25). Diarrhea.