Naltrexone is a medication prescribed to support individuals managing Alcohol Use Disorder and Opioid Use Disorder. It functions by blocking opioid effects in the brain, which helps reduce cravings and the rewarding sensations associated with substance use. The introduction of Naltrexone often results in gastrointestinal (GI) disturbances. These common initial adverse effects frequently include nausea, stomach cramping, and diarrhea.
Diarrhea as a Common Side Effect
Diarrhea is a known and common side effect reported by patients beginning treatment with Naltrexone. Clinical data indicate it occurs frequently, placing it among the most reported non-neurological side effects. This digestive upset is typically mild to moderate and is considered a temporary issue.
This gastrointestinal discomfort subsides as the body adapts to the medication, often resolving within the first few weeks of consistent treatment. While both the oral tablet and the extended-release injectable (Vivitrol) formulations can cause GI issues, the daily oral dose is associated with more frequent initial digestive upset.
In clinical trials, approximately 30% of participants taking oral Naltrexone reported diarrhea. Patients should recognize that while common, the presence of diarrhea does not indicate a failure of the medication to work.
How Naltrexone Interacts with the Gut
Naltrexone causes diarrhea because its mechanism of action extends beyond the brain to the digestive tract. The enteric nervous system, often called the “second brain,” contains a dense network of opioid receptors that Naltrexone targets.
Opioid receptors, particularly the mu-opioid type, regulate gut function. When activated, these receptors slow down intestinal motility and decrease fluid secretion, which is why opioid pain relievers often cause constipation. Naltrexone acts as an antagonist, blocking these receptors.
Blocking mu-opioid receptors in the gut removes the natural braking signal on the intestines. This leads to increased peristalsis, the wave-like muscular contraction that moves contents through the digestive system. The increased gut transit speed means less time for the colon to absorb water, resulting in the looser, more frequent stools characteristic of diarrhea.
Strategies for Managing Gastrointestinal Discomfort
Patients experiencing gastrointestinal discomfort while taking Naltrexone have several strategies to manage symptoms. A simple approach is to consistently take the oral dose at mealtime. Taking the medication with food helps buffer the digestive system and reduces irritation, minimizing symptoms like nausea and diarrhea.
Adjusting the timing of the dose may also provide relief, such as taking the tablet closer to bedtime to sleep through the peak intensity of initial side effects. Starting with a lower dose (25 milligrams) and gradually increasing it to the standard 50 milligrams can help the body adjust more smoothly.
Dietary adjustments are beneficial, focusing on foods that are easy on the stomach. A temporary bland diet can help firm up stools by focusing on foods such as:
- Bananas
- Rice
- Applesauce
- Toast
Conversely, limit irritating substances like caffeine, spicy foods, and high-fat meals. Maintaining adequate hydration is important to replace lost fluids and electrolytes. Over-the-counter anti-diarrheal medications may be an option, but a healthcare provider must be consulted first. If the diarrhea is severe, does not improve after the initial adjustment period, or if concerning symptoms like blood in the stool or signs of dehydration appear, contact a doctor immediately.