Does Glucagon-like peptide (GLP) cause rectal bleeding?

Glucagon-like Peptide (GLP) and Rectal Bleeding

Glucagon-like peptide (GLP) medications do not directly cause rectal bleeding, but they can affect bowel preparation quality for colonoscopy and may mask symptoms of underlying conditions that cause rectal bleeding. 1

GLP Medications and Gastrointestinal Effects

GLP-1 receptor agonists (GLP-1RAs) are primarily known for their gastrointestinal side effects, but these typically include:

• Nausea
• Vomiting
• Diarrhea
• Constipation
• Abdominal pain 2

These medications work by affecting gastrointestinal motility, specifically:

• Slowing gastric emptying
• Reducing colonic transit time 1

Connection to Colonoscopy and Bowel Preparation

Recent evidence shows that GLP-1RAs significantly impact bowel preparation quality for colonoscopy:

• 10% of patients on GLP-1RAs have inadequate bowel preparation compared to 4% of controls
• GLP-1RA use is an independent risk factor for inadequate bowel preparation (OR 2.7)
• This effect is seen in both diabetic and non-diabetic patients 1

Evaluation of Rectal Bleeding

If a patient on GLP-1RA presents with rectal bleeding, the medication is unlikely to be the direct cause. Instead, a systematic evaluation should be conducted:

1. Initial Assessment and Risk Stratification:

   • Calculate shock index (heart rate/systolic BP) to determine stability
   • Classify as major or minor bleeding using the Oakland score 3, 4
   • Perform digital rectal examination to identify anorectal causes 3

2. Diagnostic Approach Based on Severity:

   • For unstable patients (shock index >1): Immediate CT angiography to localize bleeding 3, 4
   • For stable patients with major bleeding (Oakland score >8): Hospital admission and colonoscopy on the next available list 3
   • For stable patients with minor bleeding (Oakland score ≤8): Outpatient colonoscopy within 2 weeks 3

Common Causes of Rectal Bleeding

The most likely causes of rectal bleeding that should be investigated include:

• Hemorrhoids (account for 42% of cases) 5
• Diverticular disease
• Angiodysplasia
• Ischemic colitis
• Colorectal cancer (found in 6% of patients with rectal bleeding) 3, 4, 5

Management Considerations

1. For patients on GLP-1RAs requiring colonoscopy:

   • Consider temporary discontinuation of GLP-1RA before bowel preparation
   • Use more aggressive bowel preparation regimens
   • Polyethylene glycol solution is preferred over glycerine or water enemas 3, 1

2. For patients with confirmed rectal bleeding:

   • Management should focus on the underlying cause rather than GLP-1RA discontinuation
   • Most cases of lower GI bleeding (80%) stop spontaneously 6
   • Endoscopic therapy is the primary treatment for active bleeding 3

Key Points for Clinicians

• GLP-1RAs do not directly cause rectal bleeding
• Rectal bleeding in patients on GLP-1RAs warrants the same thorough investigation as in any patient
• The most common causes are hemorrhoids, diverticular disease, and colorectal cancer
• GLP-1RAs can affect bowel preparation quality, which may impact diagnostic colonoscopy
• Any patient over 50 with unexplained rectal bleeding should undergo colonoscopy within 2 weeks 3

In conclusion, while GLP-1 medications can affect gastrointestinal motility and bowel preparation quality, they are not directly associated with rectal bleeding. Any rectal bleeding should be thoroughly investigated according to standard protocols to identify and treat the underlying cause.