Dicyclomine Drug Interactions: What to Avoid and What to Tell Your Doctor

Dicyclomine has more than 100 documented drug interactions — mostly due to its anticholinergic mechanism. Most are not dangerous in typical doses, but some combinations require caution or outright avoidance. This guide covers the most clinically important interactions for patients taking dicyclomine for IBS.

Why Does Dicyclomine Have So Many Drug Interactions?

The large number of interactions stems from dicyclomine's anticholinergic mechanism. Because muscarinic acetylcholine receptors are found throughout the body, any other medication that also affects this system — or that depends on it — can interact with dicyclomine. The most common interaction type is additive anticholinergic effects, where two drugs together cause more side effects than either would alone.

Contraindicated Combinations (Avoid)

Pramlintide (Symlin): Contraindicated. Both drugs inhibit GI motility through synergistic mechanisms. The combination can severely impair gut movement, potentially causing dangerous paralytic ileus.

High-Risk Interactions: Avoid or Use Alternative

Glucagon: Additive inhibition of GI motility. Discontinue dicyclomine or use an alternative if glucagon administration is planned.

Revefenacin (Yupelri), umeclidinium, sofpironium (topical), glycopyrronium topical: Other anticholinergic agents — additive anticholinergic effects. Avoid combining with dicyclomine.

Moderate Interactions: Use With Caution

Other anticholinergic medications: This includes many common drug classes — antihistamines (like diphenhydramine/Benadryl), tricyclic antidepressants (amitriptyline, nortriptyline), bladder medications (oxybutynin, tolterodine), antipsychotics, and certain Parkinson's medications. Combining any of these with dicyclomine amplifies the anticholinergic side effects — especially dry mouth, constipation, urinary retention, blurred vision, confusion, and heart rate changes.

Metoclopramide (Reglan): Pharmacodynamic antagonism — dicyclomine reduces GI motility while metoclopramide increases it. These drugs work against each other. Using them together reduces the effectiveness of both.

Antiglaucoma medications: Dicyclomine may increase intraocular pressure and antagonize the effects of glaucoma drugs. This is particularly significant — if you have glaucoma, you should not take dicyclomine at all.

Digoxin (slow-dissolving formulations): Dicyclomine slows GI transit, which can increase digoxin absorption from slow-dissolving tablets, potentially raising digoxin levels. If you take digoxin, tell your prescriber and monitor for digoxin toxicity signs (nausea, visual changes, irregular heartbeat).

Opioid pain medications: Additive CNS depression and additive reduction of GI motility. The combination increases risk of constipation and CNS sedation.

Sedatives, sleeping pills, benzodiazepines, muscle relaxers: Additive CNS sedation. The combination can significantly increase drowsiness and impair coordination. Use with extreme caution; avoid driving.

Alcohol: Additive CNS depression. Even moderate alcohol use while taking dicyclomine may significantly increase dizziness and drowsiness.

Antacids (calcium carbonate, magnesium hydroxide, etc.): Antacids interfere with the absorption of dicyclomine from the gut. If you take antacids, take them at least 2 hours before or after dicyclomine to avoid reducing its effectiveness.

Levodopa (for Parkinson's): Complex interaction — at normal doses, anticholinergics can slightly enhance levodopa effects. At higher doses, anticholinergics can reduce levodopa absorption. Also note that anticholinergics can worsen tardive dyskinesia.

Anticholinergic Burden: The Cumulative Risk

One of the most important concepts with dicyclomine interactions is "anticholinergic burden" — the cumulative anticholinergic effect of all the medications a patient takes. Many common drugs have anticholinergic properties that add up. Common culprits include:

Diphenhydramine (Benadryl) — in allergy meds and sleep aids

Tricyclic antidepressants (amitriptyline, imipramine)

Overactive bladder drugs (oxybutynin, tolterodine, solifenacin)

Certain antipsychotics (quetiapine, olanzapine, clozapine)

This is especially important for elderly patients, who are more sensitive to these effects and may be on multiple anticholinergic medications simultaneously.

What Should I Tell My Doctor and Pharmacist?

Before starting dicyclomine, tell your doctor and pharmacist:

Every prescription medication you take (including inhalers, patches, and injections)

All OTC medications, including antihistamines, sleep aids, and antacids

All supplements and herbal products

Whether you have glaucoma, an enlarged prostate, urinary problems, or myasthenia gravis

The Bottom Line

The most clinically important dicyclomine interactions involve additive anticholinergic effects (especially with antihistamines, TCAs, and bladder medications), reduced motility combinations (with pramlintide), and antagonism with antiglaucoma medications. Always do a full medication review with your pharmacist when starting dicyclomine. For more on side effects, see our complete guide to dicyclomine side effects.