Feeling nausea or stomach discomfort after using eye drops is a common, recognized medical phenomenon. While the active drug ingredients are designed to work locally on the eye, an excess amount of medication can travel beyond the surface and enter the rest of the body. This unintended spread is known as systemic absorption. When systemic absorption occurs, the medication interacts with other organ systems, including the gastrointestinal (GI) tract, leading to side effects like stomach upset, cramping, or nausea.
The Anatomy That Links the Eye and the Gut
The connection between the eye and the digestive system is a direct anatomical pathway. The ocular surface can only hold a small volume (typically 10 to 15 microliters), but a standard eye drop often contains about 40 microliters. The excess liquid drains away through a specialized system called the nasolacrimal duct.
This duct, also known as the tear duct, starts in the inner corner of the eye and leads down into the nasal cavity. The medication-containing liquid mixes with mucus and saliva, eventually being swallowed. Once swallowed, the drug enters the stomach and the gastrointestinal system, where it can cause localized irritation or be absorbed into the bloodstream.
A significant issue with this route is that the drug bypasses the liver’s natural filtration process. Oral medications travel directly to the liver, which breaks down a large portion of the drug through first-pass metabolism. Because eye drops enter the bloodstream through the highly vascularized nasal and pharyngeal mucosa, they avoid this initial liver breakdown. This leads to a higher concentration of the active drug circulating in the body than expected, increasing the likelihood of systemic side effects affecting the GI tract. Up to 80% of the applied drug can diffuse into the systemic circulation through this pathway.
Specific Medication Types Known to Cause GI Upset
Certain ophthalmic medications are more likely to cause gastrointestinal side effects due to their powerful systemic effects. Glaucoma medications, for instance, are common culprits because they contain potent compounds.
Carbonic Anhydrase Inhibitors (CAIs)
CAIs, a class of glaucoma drops, are known to cause stomach upset, nausea, and changes in taste, often resulting in a metallic or bitter sensation.
Steroid Eye Drops
Steroid eye drops, prescribed after surgery or for severe inflammation, can also contribute to stomach distress. When absorbed systemically, corticosteroids can irritate the stomach lining, potentially causing acid buildup, nausea, or stomach cramps and discomfort.
Prostaglandin Analogues
This group, also used to treat glaucoma, has been linked to GI issues like nausea, gastric reflux, and general malaise. These drugs can influence smooth muscle contraction, which may contribute to symptoms like esophageal spasm or general GI distress in sensitive individuals. The potential for GI side effects is magnified because the drug concentration is formulated for intense local action, not for systemic tolerance.
Simple Techniques to Prevent Systemic Absorption
Simple behavioral modifications can significantly reduce the amount of medication that reaches the nasolacrimal duct and the GI tract. The most effective technique is called punctal occlusion, which involves physically blocking the tear duct immediately after administering the drop.
To perform punctal occlusion, gently press a finger against the inner corner of the eyelid, near the bridge of the nose, immediately after placing the drop in the eye. Applying gentle, firm pressure for one to two minutes prevents the solution from draining into the tear duct. This action forces the drug to remain on the eye’s surface, maximizing its local effect while minimizing systemic absorption.
Other steps also help reduce drainage. Keep the eye closed for about one to two minutes after instillation and avoid blinking, as blinking actively pumps medication into the drainage system. Since standard eye drop volume exceeds the eye’s capacity, use only one drop per dose. Blotting any excess liquid from the outside of the eyelid with a clean tissue can also prevent runoff into the tear duct. Following these instructions can significantly lower the drug concentration in the bloodstream, often resolving unwanted stomach side effects.