Opioid-induced constipation (OIC) is a common condition affecting individuals who take opioid medications for pain relief. It is characterized by changes in bowel habits, such as fewer bowel movements, difficulty passing stool, or a feeling of incomplete evacuation. This type of constipation directly results from the opioid’s interaction with the digestive system. Many people, between 40% and 80% of those using opioids for chronic pain, experience OIC.
What Causes Opioid-Induced Constipation
Opioids exert their effects by binding to mu-opioid receptors, found throughout the body, including the gastrointestinal (GI) tract. These receptors, present in the stomach and upper large intestine (proximal colon), regulate bowel movements. When opioids attach to these receptors, they disrupt the normal functioning of the digestive system.
This interaction leads to several physiological changes that contribute to constipation. Opioids slow down the movement of food through the digestive tract, a process called peristalsis, by inhibiting the release of certain neurotransmitters like acetylcholine. This delayed transit time allows more water to be absorbed from waste material in the intestines, resulting in harder, drier stools that are difficult to pass. Opioids also increase the tone of the anal sphincter, further impeding the defecation reflex.
Lifestyle Approaches to Prevention
Adopting certain lifestyle practices can significantly help in preventing or reducing the severity of opioid-induced constipation. Increasing dietary fiber intake is a primary strategy, as fiber adds bulk to stools and helps them retain water, making them softer and easier to pass. Adults need between 25 to 35 grams of fiber per day, obtainable from foods like fruits (e.g., apples, pears, prunes), vegetables (e.g., leafy greens, broccoli), and whole grains. Bulk-forming laxatives, which are fiber supplements, should generally be avoided in OIC as they can worsen abdominal pain and potentially lead to bowel obstruction if peristalsis is severely inhibited by opioids.
Adequate fluid consumption is equally important for fiber to be effective and to prevent dehydration, which can worsen constipation. Drinking 8 to 10 glasses of clear liquids, such as water, juice, or clear broths, daily is recommended. Incorporating water with meals and between them can also be beneficial, while beverages containing caffeine or alcohol should be limited as they can contribute to dehydration. Regular physical activity also stimulates bowel movements and can help alleviate constipation. Even modest exercise, such as short walks, can promote intestinal motility and reduce the risk of OIC.
Over-the-Counter Remedies
When lifestyle adjustments alone are insufficient, several over-the-counter (OTC) medications can provide relief for opioid-induced constipation. Stool softeners, such as docusate sodium, work by increasing the amount of water absorbed into the stool, making it softer and easier to pass. These are recommended for preventing constipation, particularly when starting opioid therapy.
Osmotic laxatives, including polyethylene glycol (PEG) and milk of magnesia, draw water into the intestines, which helps to soften the stool and stimulate bowel movements. PEG is widely available and considered a first-line option for chronic constipation due to its effectiveness and few side effects. Stimulant laxatives like senna and bisacodyl directly act on the intestinal muscles, increasing contractions and speeding up bowel movements. While effective, stimulant laxatives are recommended for short-term use, as prolonged use can lead to dependency or electrolyte imbalances.
Prescription Medications
For individuals whose opioid-induced constipation does not respond adequately to lifestyle changes or over-the-counter remedies, prescription medications specifically designed for OIC are available. Peripheral Acting Mu-Opioid Receptor Antagonists (PAMORAs) represent a class of these medications, including drugs like methylnaltrexone, naloxegol, and naldemedine. These medications work by blocking the effects of opioids on the mu-opioid receptors in the gut, thereby counteracting the constipating effects without reducing the opioid’s pain-relieving properties in the central nervous system.
Methylnaltrexone is available in both oral tablet and subcutaneous injection forms, while naloxegol and naldemedine are taken orally. Another type of prescription medication, chloride channel activators like lubiprostone, works by increasing fluid secretion into the intestines, which helps to soften stool and improve its passage. Linaclotide, a guanylate cyclase-C agonist, also acts by increasing intestinal fluid secretion and accelerating transit time. Consult a healthcare provider to determine the most appropriate prescription option, as these medications may have side effects such as abdominal pain, diarrhea, or nausea.