Does the body absorb eye drops? The surprising truth about systemic drug absorption

October 9, 2025 •

4 min read

Up to 80% of an instilled eye drop can enter the body's systemic circulation, not just remain on the ocular surface. So, does the body absorb eye drops? The answer is a surprising and pharmacologically significant 'yes', a concept that can have important implications for patient health.

Quick Summary

Ophthalmic medications are absorbed systemically through the nasolacrimal duct into the highly vascular nasal mucosa. Proper instillation technique, such as punctual occlusion, is crucial to minimize unwanted drug exposure and potential systemic side effects.

Key Points

Systemic Absorption is Common: Most of an administered eye drop, sometimes up to 80%, does not stay in the eye but is absorbed into the bloodstream via the nasolacrimal duct.
Main Route of Absorption: The nasolacrimal duct drains eye drops into the nasal cavity, where the highly vascular mucosa allows for rapid entry into the systemic circulation.
Minimizing Systemic Exposure: Techniques like punctal occlusion (pressing on the tear duct) and gentle eye closure after instillation can significantly reduce the amount of drug absorbed systemically.
Potential for Side Effects: Due to systemic absorption, eye drops can cause side effects elsewhere in the body, such as cardiac effects from beta-blockers or drowsiness from certain medications.
Taste is a Sign of Absorption: If you can taste your eye drops in the back of your throat, it is a clear sign that the medication has drained into your nasolacrimal duct and reached the nasal cavity.
Proper Technique is Key: Patient administration technique is a primary determinant of drug delivery, and correct usage is essential for maximizing therapeutic effect and minimizing systemic risk.

The Journey of an Eye Drop: From Eye to Bloodstream

Many people assume that eye drops act only on the surface of the eye, providing localized treatment without affecting the rest of the body. In reality, a significant portion of an administered eye drop does not stay in the eye but is absorbed into the bloodstream. This systemic absorption can lead to side effects in other parts of the body, a key concern in pharmacology and patient care.

The Anatomy of Absorption: Where Do Eye Drops Go?

To understand why the body absorbs eye drops, one must consider the anatomy of the eye's drainage system. The journey of an eye drop begins on the ocular surface. However, the conjunctival sac—the pocket between the eyeball and the eyelid—can only hold a small volume of fluid, about 7-10 microliters. Since a typical commercial eye drop contains 25-50 microliters, a large portion of the medication immediately overflows, either spilling out or entering the main route for systemic absorption: the nasolacrimal drainage system.

This system consists of the lacrimal puncta (small openings in the inner corners of the eyelids), the canaliculi, and the nasolacrimal duct, which empties into the nasal cavity. The nasal mucosa is highly vascularized, meaning it contains a dense network of blood vessels. When the eye drops travel through this duct, they come into contact with the nasal mucosa, and the drug is rapidly absorbed directly into the bloodstream, bypassing the liver's first-pass metabolism. This is also the reason some people can taste their eye drops in the back of their throat.

Factors Influencing Systemic Absorption

Several factors can influence the extent to which eye drops are absorbed systemically. A better understanding of these factors allows for more effective treatment with fewer side effects.

Physicochemical Properties of the Drug: The chemical characteristics of the drug play a crucial role. Lipophilic (fat-soluble) drugs can easily penetrate the corneal epithelium, while hydrophilic (water-soluble) drugs have a harder time. Both types, however, can be absorbed through the conjunctiva and nasolacrimal duct. Some drugs, like beta-blockers, are highly lipophilic and have particularly high systemic absorption.
Drug Concentration and Volume: Eye drop formulations often use high concentrations of active ingredients to ensure enough medication reaches the targeted ocular tissues. This high concentration, combined with the large volume of a typical drop, increases the amount of drug available for systemic absorption via the nasolacrimal duct.
Patient Technique: How a patient administers the drops is one of the most critical factors. Blinking excessively, for example, can pump the drug more quickly into the nasolacrimal system. Conversely, using proper technique can significantly reduce systemic exposure.

Comparison of Absorption Routes


Route of Absorption	Mechanism	Impact on Ocular Bioavailability	Impact on Systemic Absorption
Corneal Route	Drug diffuses directly through the cornea's layers into the anterior chamber.	Very low (typically <5%), as the cornea is a major barrier.	Negligible, as drug is contained within the eye initially.
Non-Corneal (Conjunctival) Route	Drug is absorbed across the conjunctiva and sclera into the surrounding tissues and local circulation.	Important for certain hydrophilic drugs or large molecules.	Substantial, especially when coupled with nasolacrimal drainage.
Nasolacrimal Duct	Excess fluid and drops drain into the nasal cavity, where absorption occurs via the vascular mucosa.	Wastes medication, reducing the amount available for ocular tissues.	Major route of rapid systemic absorption, bypassing first-pass metabolism.
Oral Ingestion	Swallowing eye drops that drain into the throat, leading to absorption via the gastrointestinal tract.	Inadvertent, represents wasted medication.	Can lead to toxic levels, especially in children, depending on the drug.

Minimizing Systemic Absorption of Eye Drops

For most ophthalmic medications, the goal is to maximize local absorption in the eye while minimizing systemic exposure. This can prevent unnecessary side effects. Healthcare providers often recommend a technique called punctal occlusion. To perform this:

Instill one eye drop into the conjunctival sac.
Immediately after, close the eyelid gently (do not squeeze).
Use a clean finger to apply light pressure to the inner corner of the eyelid, next to the nose.
Maintain this gentle pressure for two to three minutes.

This technique physically blocks the opening of the nasolacrimal duct, preventing the medication from draining into the nose. This forces the drop to remain on the ocular surface for a longer period, increasing local absorption and reducing systemic uptake. If a patient is prescribed more than one type of drop for the same eye, they should wait at least five to ten minutes between applications to prevent the second drop from washing out the first.

Systemic Side Effects: A Pharmacological Reality

The systemic absorption of eye drops can lead to a variety of side effects depending on the medication. For example, beta-blocker eye drops prescribed for glaucoma can cause systemic effects such as slowed heart rate (bradycardia), low blood pressure (hypotension), and fatigue, particularly in patients with pre-existing heart or lung conditions. In children, who are at a higher risk due to their smaller size, certain eye drops can cause drowsiness, lethargy, or even more severe reactions. Awareness of these possibilities is essential for both prescribing physicians and patients using ophthalmic medications.

Conclusion

The body unequivocally absorbs eye drops, primarily through the vascular nasal mucosa after draining via the nasolacrimal duct. While the eye has protective barriers that limit local absorption, these same mechanisms lead to significant systemic drug exposure. Patients and healthcare professionals must be aware of this process to ensure safe and effective treatment. By utilizing proper instillation techniques like punctal occlusion, it is possible to minimize systemic absorption, reduce the risk of unwanted side effects, and optimize the medication's therapeutic effect where it is needed most: in the eye. For those using eye drops, understanding this small but mighty journey is key to better managing their health. Further information on pharmacology and drug interactions can be found in authoritative medical resources such as those from the National Institutes of Health (NIH).

Frequently Asked Questions

You can taste your eye drops because they drain through the nasolacrimal duct, which connects the corner of your eye to your nose and throat. The drops travel down this passage and can be tasted on your palate.

A surprisingly high percentage of an eye drop can be absorbed systemically. Estimates suggest that only a small portion, often less than 5-10%, remains on the eye's surface, while a major fraction can enter the bloodstream.

The most effective method is punctal occlusion. This involves closing your eye and applying gentle pressure with a clean finger to the inner corner of your eyelid (near your nose) for two to three minutes after instillation.

Yes, depending on the medication, systemic absorption can cause significant side effects. For example, beta-blocker eye drops for glaucoma can cause bradycardia (slow heart rate) and fatigue. Other drugs may cause different systemic reactions.

Yes, infants and the elderly are particularly at risk. Infants have a smaller body mass, and doses are not typically weight-adjusted. The elderly often use multiple medications, increasing the risk of drug interactions and adverse effects.

Yes. If you need to use more than one type of eye drop in the same eye, you should wait at least five to ten minutes between applications. This prevents the first drop from being washed out by the second.

While small amounts are typically not dangerous for adults, certain eye drop medications can be toxic if swallowed, especially by children. It is always best to prevent ingestion and to contact a medical professional if a significant amount is consumed.