Know What Interacts With Timolol Before You Start

Timolol is a nonselective beta-blocker used as eye drops for glaucoma and as oral tablets for blood pressure and migraines. Because it affects your heart, lungs, and blood vessels, it can interact with a number of other medications — sometimes dangerously.

Even timolol eye drops can cause drug interactions, because the medication gets absorbed into your bloodstream through the eye.

Here's what you need to know about timolol drug interactions, including which medications to avoid and what to tell your doctor.

How Drug Interactions Work With Timolol

Drug interactions happen in a few ways:

• Additive effects: Another medication does the same thing timolol does (like slowing the heart), so the combined effect becomes too strong.
• Blocking metabolism: Some drugs slow down the way your body breaks down timolol, causing higher-than-expected levels in your blood.
• Opposing effects: A medication may work against timolol, making one or both drugs less effective.

Timolol is metabolized partly by the liver enzyme CYP2D6. Drugs that inhibit this enzyme can increase timolol levels in your body and amplify side effects.

Major Drug Interactions

These combinations should generally be avoided or require careful monitoring by your doctor:

Calcium Channel Blockers

Verapamil (Calan, Verelan) and diltiazem (Cardizem, Tiazac) combined with timolol can cause:

• Dangerously slow heart rate (severe bradycardia)
• Heart block (AV block)
• Heart failure

These are the most clinically significant interactions with timolol. If you need both a calcium channel blocker and timolol, your doctor will monitor you closely — but the combination of verapamil with timolol is generally avoided.

Other Beta-Blockers

Taking another beta-blocker (like metoprolol, atenolol, or propranolol) along with timolol eye drops creates additive effects — excessively slowing your heart rate and lowering blood pressure. Always tell your eye doctor if you're already taking an oral beta-blocker.

Clonidine (Catapres)

If you take clonidine for blood pressure and stop it suddenly while on timolol, you can experience dangerous rebound hypertension — a sudden spike in blood pressure. If both drugs need to be discontinued, timolol should be stopped several days before clonidine.

Digitalis Glycosides

Digoxin (Lanoxin) combined with timolol can cause excessive bradycardia and heart block. Both drugs slow the heart, and together the effect can be dangerous.

CYP2D6 Inhibitors

These medications slow down timolol's metabolism, potentially increasing its levels and side effects:

• Quinidine (antiarrhythmic)
• Fluoxetine (Prozac) — SSRI antidepressant
• Paroxetine (Paxil) — SSRI antidepressant

If you're prescribed one of these with timolol, your doctor may need to adjust doses.

Epinephrine

Timolol can reduce the effectiveness of epinephrine (EpiPen) in treating severe allergic reactions (anaphylaxis). If you carry an EpiPen and use timolol, make sure all your healthcare providers know. You may need a higher dose of epinephrine in an emergency.

Moderate Drug Interactions

These interactions are less dangerous but still important to know about:

Insulin and Oral Diabetes Medications

Timolol can mask the symptoms of low blood sugar (hypoglycemia), particularly rapid heartbeat and trembling. This is especially important for people taking insulin, metformin, glipizide, or other diabetes medications. You'll need to monitor your blood sugar more carefully.

NSAIDs (Anti-Inflammatory Pain Relievers)

Medications like ibuprofen (Advil, Motrin) and naproxen (Aleve) may reduce timolol's blood pressure-lowering effect. If you take oral timolol for hypertension and regularly use NSAIDs, your blood pressure control may suffer.

MAO Inhibitors

Monoamine oxidase inhibitors like phenelzine (Nardil) and tranylcypromine (Parnate) combined with timolol may cause significant increases in blood pressure.

Reserpine

This older blood pressure medication can cause additive hypotension (low blood pressure) and excessive bradycardia when used with timolol.

Supplements and Over-the-Counter Drugs to Watch

Don't forget about these common items that can interact with timolol:

• Decongestants containing pseudoephedrine or phenylephrine (like Sudafed) — can counteract timolol's blood pressure-lowering effect.
• Eye drops containing other beta-blockers or sympathomimetics — check with your pharmacist before combining eye medications.
• Herbal supplements: St. John's wort may affect timolol metabolism. Hawthorn may increase blood pressure-lowering effects.

Food and Drink Interactions

There are no significant food interactions with timolol. Oral tablets can be taken with or without food. There are no restrictions on alcohol specifically related to timolol, though alcohol can lower blood pressure and may add to dizziness or lightheadedness — use caution.

What to Tell Your Doctor

Before starting timolol, give your doctor a complete list of:

• All prescription medications — especially heart drugs, blood pressure medications, antidepressants, and diabetes medications
• Over-the-counter medications — including pain relievers, cold medicines, and allergy medications
• Eye drops — other glaucoma medications or redness-reducing drops
• Supplements and herbal products
• Medical conditions — especially asthma, COPD, diabetes, heart failure, or depression

If you're having surgery (including dental surgery), tell the surgeon and anesthesiologist that you take timolol. Beta-blockers can interact with anesthesia medications.

For more about timolol's side effects and how it works, check our other guides.

Final Thoughts

Timolol is a safe and effective medication when used correctly, but its interactions with heart medications, antidepressants, and diabetes drugs are important to know about. The single most important thing you can do is keep your doctors and pharmacists informed about every medication you take — including eye drops.

Looking for timolol? Use Medfinder to check pharmacy availability near you.