Constipation and Melanoma Treatment: Is It Common and How To Manage It

Constipation can happen during melanoma treatment, most often from chemotherapy and pain medicines, and it can usually be managed with simple steps and safe medications. ^[1] Constipation means fewer bowel movements than usual, hard stools, or straining to pass stools. ^[1]

Why Constipation Happens

• Chemotherapy effects: Some chemotherapy drugs slow bowel movement, leading to hard or infrequent stools. ^[1]
• Pain medicines (opioids): Opioids commonly cause constipation and often need a preventive bowel plan if used for more than a few days. ^{[2] [3]}
• Diet, fluids, and activity: Lower fiber intake, dehydration, and reduced activity during treatment can also contribute. ^[1]

Immunotherapy for melanoma more often causes diarrhea or bowel inflammation (colitis), but constipation can occur from other supportive medications used alongside treatment. If you ever develop persistent diarrhea, blood in stool, or severe abdominal pain during immunotherapy, contact your team promptly because it could be immune-related colitis. ^[4]

First-Line Prevention and Self-Care

• Hydration: Aim for about 8 cups (8-ounce) of liquids daily if your care team agrees. Warm liquids (like tea) can help kick-start a bowel movement. ^{[1] [5]}
• Fiber: Include fruits, vegetables, beans, whole grains, nuts, and seeds as tolerated to increase stool bulk. ^{[1] [5]}
• Gentle activity: Walking or light exercise can stimulate bowel motility. Check with your team before increasing activity if you’re feeling weak. ^{[1] [5]}
• Routine: Try going to the bathroom around the same time each day and don’t ignore the urge to go. ^[6]
• Comfort measures: Ensure privacy, consider a footstool to raise your knees on the toilet, and give yourself unhurried time. [PM24]

Over‑the‑Counter Options

If lifestyle steps aren’t enough, several OTC medications can be used safely and are commonly recommended:

• Stimulant laxatives (senna, bisacodyl): Help the bowel contract; often used first, especially if you’re on opioids. ^{[2] [3]}
• Osmotic laxatives (polyethylene glycol/PEG, magnesium oxide): Draw water into the bowel to soften stool; PEG is strongly supported for chronic constipation when OTC options are needed. [PM25] [PM26] [PM15]
• Stool softeners (docusate): May be used with stimulants; using stool softeners or fiber alone without another laxative is generally not advised for opioid-related constipation. ^{[2] [3]}

Always check with your oncology team before starting new medications, especially if you have kidney issues, are on fluid restrictions, or have been told to limit fiber during episodes of diarrhea. ^[1]

If You’re Taking Opioids

When opioids are prescribed for cancer pain, a preventive bowel regimen is usually recommended from day one, because treating established opioid-induced constipation (OIC) is harder than preventing it. ^{[2] [3]}

• Start with a stimulant laxative (senna) ± a stool softener, and add an osmotic agent (like PEG) if needed. ^{[2] [3]}
• If constipation persists despite laxatives, peripherally acting mu‑opioid receptor antagonists (PAMORAs) such as naldemedine, naloxegol, or methylnaltrexone can be effective. These target opioid effects in the gut without reducing pain control. [PM24]

Special Notes for Immunotherapy

• Watch for diarrhea or blood in stool, fever, or severe cramping, which may signal immune-related colitis rather than simple constipation. This needs prompt evaluation and different treatment. ^[4]
• If you are having diarrhea from immunotherapy, your team may advise temporary low-fiber, bland foods; once diarrhea resolves, you can gradually return to fiber for constipation prevention as guided. ^{[7] [4]}

When To Call Your Care Team

• No bowel movement for 3 days despite using laxatives or worsening pain/bloating. ^[1]
• Vomiting, severe abdominal pain, or inability to pass gas, which could indicate a blockage. ^[1]
• New diarrhea, black or bloody stools, or fever during immunotherapy. ^[4]

Practical Step‑By‑Step Plan

1. Hydrate and move: 8 cups fluids daily and gentle walks if you’re able. ^[1]
2. Add fiber gradually: Fruits, vegetables, whole grains; consider prunes or prune juice. ^[1]
3. Set a bathroom routine: Same time daily; don’t delay the urge to go. ^[6]
4. Start OTCs if needed: Senna at night; add PEG in the morning; adjust based on response. ^{[2] [3]} [PM15]
5. On opioids: Begin a prophylactic bowel regimen with a stimulant laxative right away; discuss PAMORAs if constipation continues. ^{[2] [3]} [PM24]
6. Monitor red flags: Call your team for severe symptoms or signs of immune-related colitis. ^[4]

Key Takeaway

Constipation can be a common and manageable side effect during melanoma care, especially with chemotherapy and opioids; a mix of fluids, fiber, movement, and the right laxatives plus early prevention when using opioids usually helps. ^{[1] [2] [3]} If symptoms persist or you notice warning signs, it’s important to reach out to your oncology team promptly. ^{[1] [4]}