Does co-codamol (codeine and paracetamol) cause diarrhea?

Co-codamol Does Not Cause Diarrhea—It Causes Constipation

Co-codamol (codeine plus paracetamol) does not cause diarrhea; rather, the codeine component is an antidiarrheal agent that commonly causes constipation as a side effect. 1

Codeine's Mechanism and Gastrointestinal Effects

Antidiarrheal Properties

• Codeine is specifically used as a therapeutic agent to treat diarrhea, not cause it 1
• The drug works by slowing intestinal transit time, particularly in the jejunum, which increases contact time between luminal fluid and mucosal cells 2
• Codeine does not increase the rate of intestinal absorption itself, but rather delays fluid movement through the gut, resulting in reduced stool volume 2
• At therapeutic doses of 15-30 mg taken 1-3 times daily, codeine effectively reduces stool frequency and urgency 1

Constipation as the Primary Side Effect

• Constipation is the most significant and common gastrointestinal side effect of codeine, not diarrhea 1
• This constipating effect is so pronounced that loperamide is generally preferred over codeine for treating diarrhea specifically because loperamide lacks the central nervous system effects while maintaining the gut-slowing properties 1
• Multiple guidelines note that constipation was the usual reason patients discontinued codeine therapy when used as an antidiarrheal 3

Paracetamol Component Safety

• The paracetamol (acetaminophen) component of co-codamol is not associated with diarrhea 4
• Paracetamol may cause upper GI symptoms such as abdominal pain, heartburn, nausea, or vomiting at high doses, but diarrhea is not a recognized adverse effect 4

Clinical Context

When Codeine Is Used Therapeutically

• Codeine is listed alongside loperamide, diphenoxylate, and tincture of opium as standard antidiarrheal medications in multiple clinical guidelines 1
• In short bowel syndrome, codeine may be used synergistically with loperamide to control high-output diarrhea 1
• For cancer patients with chemotherapy-induced diarrhea, codeine serves as an alternative when loperamide is insufficient 1

Important Caveats

• While codeine does not cause diarrhea, it can cause sedation and has addiction potential, which is why loperamide is preferred as first-line therapy 1
• In patients with bowel dilatation or bacterial overgrowth, antimotility agents like codeine might theoretically worsen symptoms by slowing transit excessively, but this would manifest as constipation or ileus, not diarrhea 1

If a patient taking co-codamol develops diarrhea, look for alternative causes such as infection, dietary factors, or other medications—the co-codamol itself is not the culprit and may actually be therapeutic. 1