Dicyclomine, prescribed for irritable bowel syndrome and intestinal cramping, causes side effects in a significant number of people who take it. In clinical trials at the standard dose, 40% of patients experienced dizziness and 33% had dry mouth. Most side effects stem from the drug’s anticholinergic properties, meaning it blocks a chemical messenger that controls involuntary functions like saliva production, sweating, digestion, and pupil size.
The Most Common Side Effects
Clinical trials comparing dicyclomine to placebo at 160 mg per day (the upper end of dosing) showed these side effects at notably higher rates than placebo:
- Dizziness: 40% of patients (vs. 5% on placebo)
- Dry mouth: 33% (vs. 5%)
- Blurred vision: 27% (vs. 2%)
- Nausea: 14% (vs. 6%)
- Drowsiness: 9% (vs. 1%)
- Weakness: 7% (vs. 1%)
- Nervousness: 6% (vs. 2%)
About 9% of patients in trials stopped taking dicyclomine because of side effects, compared to 2% on placebo. Beyond the list above, patients also commonly report constipation, stomach pain, gas, bloating, loss of appetite, headache, tingling, double vision, and difficulty urinating. These are all predictable consequences of blocking the same nerve signals the drug uses to calm intestinal spasms.
Why These Side Effects Happen
Dicyclomine works by blocking a type of receptor found throughout the body, not just in your gut. The same receptors that trigger intestinal cramping also control saliva production (hence dry mouth), pupil dilation (blurred vision), bladder contractions (difficulty urinating), sweat glands (reduced sweating), and parts of the brain involved in alertness (dizziness and drowsiness). The drug can’t target only your intestines, so shutting down these receptors system-wide produces a broad range of effects.
One side effect that catches people off guard is reduced sweating. Because dicyclomine impairs your body’s ability to cool itself, exercising in hot weather or spending time in high temperatures can lead to overheating, fever, or even heat stroke. This is worth paying attention to during summer months or if you work outdoors.
Serious Side Effects at Higher Doses
At higher doses or with prolonged misuse, dicyclomine can cause more alarming neurological effects. These include confusion, disorientation, hallucinations, agitation, and short-term memory loss. A case report documented a patient who developed hallucinations, euphoria, slurred speech, and loss of coordination after taking excessive amounts of the drug over an extended period, ultimately diagnosed with anticholinergic toxicity.
Dicyclomine can also precipitate two urgent conditions in susceptible people: acute narrow-angle glaucoma (a sudden, painful spike in eye pressure) and acute urinary retention (complete inability to urinate). Both require immediate medical attention. If you have a history of glaucoma or urinary problems, this drug is typically not appropriate for you.
Risks for Older Adults
The American Geriatrics Society explicitly recommends avoiding dicyclomine in adults 65 and older. It appears on the 2023 Beers Criteria, a widely used list of medications considered potentially inappropriate for older adults, classified under drugs with “strong anticholinergic activity.” The rationale is straightforward: older adults are more sensitive to anticholinergic effects like confusion, falls from dizziness, urinary retention, and constipation. The panel rated the evidence as moderate and the recommendation to avoid as strong, adding that the drug’s effectiveness in this population is uncertain to begin with.
Drugs That Make Side Effects Worse
Taking dicyclomine alongside other medications that have anticholinergic properties amplifies every side effect. The list of interacting drugs is long and includes antihistamines (like diphenhydramine), tricyclic antidepressants, certain antipsychotics, some heart rhythm medications, benzodiazepines, opioid painkillers, and MAO inhibitors. If you’re taking any of these, the combined anticholinergic load can push side effects from uncomfortable to dangerous.
Antacids also interfere with how well dicyclomine is absorbed, so they shouldn’t be taken at the same time. And if you use eye drops for glaucoma, dicyclomine works directly against them by raising intraocular pressure.
Dosing and When Side Effects Peak
Most people start at 80 mg per day (20 mg taken four times daily). After one week, the dose can be increased to 160 mg per day if side effects are tolerable. This matters because the clinical trial data showing 40% dizziness rates came from the higher dose. Many people experience milder side effects at the starting dose.
There’s an important safety boundary: no documented safety data exist for doses above 80 mg per day taken longer than two weeks. If the drug isn’t working within two weeks, or if side effects force the dose below 80 mg daily, guidelines call for discontinuing it rather than continuing indefinitely at a low, potentially ineffective dose.
Who Should Not Take Dicyclomine
Dicyclomine is contraindicated in several specific situations: infants under 6 months, nursing mothers, and anyone with glaucoma, myasthenia gravis (a neuromuscular condition), gastrointestinal obstruction, severe ulcerative colitis, reflux esophagitis, or obstructive urinary tract problems. It’s also prohibited in people with unstable cardiovascular status from acute bleeding.
Practical Tips for Managing Side Effects
Dry mouth is the most persistent nuisance for many people. Sipping water frequently, chewing sugar-free gum, and using saliva substitutes can help. For constipation, staying well-hydrated and eating high-fiber foods counteracts the slowing of your digestive tract. Drowsiness and blurred vision are strongest in the first few days and often improve as your body adjusts, but you should avoid driving or operating machinery until you know how the drug affects you.
Because the drug impairs sweating, staying cool in warm environments is genuinely important, not just a theoretical warning. If you notice you’re not sweating during activity on a hot day, move to a cooler area. Monitoring your urine output is also worthwhile, since difficulty urinating can develop gradually and worsen without obvious warning signs early on.