What Happens If You Drink Eyedrops?

Drinking eyedrops, even a small amount, can cause a dangerous drop in heart rate and blood pressure, sometimes severe enough to require emergency medical care. The culprit in the most common over-the-counter redness-relief drops is tetrahydrozoline, a drug designed to constrict tiny blood vessels on the eye’s surface. Applied topically, only a trace enters the bloodstream. Swallowed, the full dose hits the body at once, and the consequences can range from drowsiness and a dangerously slow pulse to complete heart block.

Why a Tiny Bottle Can Be So Dangerous

The ingredient that makes redness-relief eyedrops work is tetrahydrozoline, an imidazoline compound found in products like Visine and several store-brand equivalents.¹ When a drop lands on the eye, tetrahydrozoline squeezes the small blood vessels on the surface, clearing redness. The dose per drop is minuscule, and very little gets past the eye’s membranes into the rest of the body. Swallowing the liquid changes the equation entirely. The gastrointestinal tract absorbs the drug efficiently, delivering a systemic dose far larger than anything the eye would ever see.

What makes this particularly deceptive is the size of the bottle. A standard eyedrop bottle holds about 15 mL, which barely qualifies as a sip. Yet that small volume contains enough tetrahydrozoline to produce serious symptoms in an adult and potentially life-threatening effects in a child. The drug is concentrated at 0.05% in most formulations, which sounds negligible until you consider that it acts on central receptors in the brain and cardiovascular system at very low blood levels.

What Happens to the Heart

The most alarming effect of swallowed tetrahydrozoline is what it does to heart rhythm and blood pressure. The drug activates alpha-adrenergic receptors in the central nervous system, which sends a signal to slow the heart and relax blood vessels. In clinical terms, this produces bradycardia (an abnormally slow heart rate) and hypotension (dangerously low blood pressure).¹

In a published case report, a 76-year-old man who swallowed roughly 120 mL of tetrahydrozoline solution (the equivalent of about eight bottles of Visine) in a suicide attempt developed complete heart block within 24 hours. His heart’s electrical conduction system essentially stopped relaying signals from the upper chambers to the lower chambers. ECG monitoring also showed prolongation of the QT interval, a change in the heart’s electrical cycle that raises the risk of a fatal arrhythmia.¹ Even after the acute crisis resolved, follow-up readings continued to show first-degree heart block and persistent QT prolongation, meaning the electrical disturbance lingered.

The cardiovascular effects are not limited to extreme overdoses. Smaller amounts can still slow the heart enough to cause dizziness, fainting, and a sense that something is very wrong. For anyone with a pre-existing heart condition or who takes medications that already slow heart rate (like beta-blockers), even a modest ingestion could push the heart into a dangerous rhythm.

Effects on the Brain and Breathing

Because tetrahydrozoline crosses into the central nervous system, swallowing it can mimic sedative poisoning. Drowsiness, lethargy, and a depressed level of consciousness are commonly reported. In some cases, people become so sedated that they are difficult to rouse, a state that can look frighteningly similar to a drug overdose or a neurological emergency.²

Breathing can slow as well. The same central mechanism that depresses consciousness also dampens the brain’s respiratory drive. In younger children or elderly adults, this respiratory depression may progress to the point where the person needs assistance breathing. Body temperature can drop, too, because the drug disrupts the normal thermoregulatory signals that keep the body warm. The combination of a slow heart, low blood pressure, shallow breathing, and falling body temperature makes eyedrop poisoning a genuine medical emergency, not the harmless prank that pop culture sometimes portrays.

Children Are at Especially High Risk

Toddlers and infants face the greatest danger from accidental eyedrop ingestion, for the simple reason that even a few milliliters represent a much larger dose relative to their body weight. Small amounts of tetrahydrozoline swallowed by a young child can cause severe central nervous system depression, slow breathing, a drop in heart rate, and dangerously low blood pressure, frequently resulting in emergency department visits and hospital admissions.³

Young children are also less able to communicate what they’ve swallowed, which can delay recognition. A toddler who suddenly becomes very sleepy and difficult to wake, with cool skin and a weak pulse, may not immediately prompt suspicion of eyedrop ingestion unless a caregiver notices a bottle within reach. Poison control centers in the United States receive a steady stream of calls about children who have gotten into eyedrops, and the advice is consistent: any ingestion by a small child warrants an immediate call to poison control or a trip to the emergency room, regardless of how little they seem to have swallowed.

This is a good reason to store redness-relief eyedrops out of children’s reach, the same way you would treat any medication. The childproof cap on most eyedrop bottles is not particularly robust, and the liquid inside does not taste strongly enough to deter a curious toddler.

Not All Eyedrops Are the Same

Tetrahydrozoline gets most of the attention because it is the active ingredient in the most popular over-the-counter redness-relief drops, but other types of eyedrops carry their own risks when swallowed.

Atropine eyedrops, prescribed by eye doctors to dilate the pupil or treat certain conditions, contain a drug that blocks the parasympathetic nervous system. A French forensic case report described a situation where atropine eyedrops were emptied into another person’s drink. The victim was found with a rectal temperature above 41 °C, widely dilated pupils, and blood concentrations of atropine consistent with a dose at least 20 times higher than what would be given therapeutically.⁴ Atropine poisoning produces essentially the opposite cardiac picture from tetrahydrozoline: the heart races rather than slows, the body overheats, and the person becomes confused or agitated. It can be just as lethal.

Brimonidine, another prescription drop used to lower eye pressure in glaucoma, belongs to the same imidazoline family as tetrahydrozoline and produces a similar set of problems when swallowed. Data from accidental ingestions in dogs showed high rates of bradycardia, depression, low blood pressure, and hypothermia.⁵ While the veterinary data doesn’t translate directly to humans, the mechanism is the same, and human case reports of brimonidine poisoning in children describe a very similar clinical picture to tetrahydrozoline ingestion.

Artificial tears and lubricating drops that contain no active vasoconstrictor or medication are the one major exception. These products are mostly water, electrolytes, and thickening agents. Swallowing a small amount would likely cause nothing more than mild stomach upset, if that. The risk is specifically tied to drops that contain a pharmacologically active drug.

The Pop Culture Myth and the Criminal Reality

For decades, a persistent myth circulated that slipping eyedrops into someone’s drink would cause nothing worse than diarrhea, a “prank” depicted in movies and described in frat-house lore. This is dangerously wrong. There is no reliable evidence that tetrahydrozoline causes significant diarrhea when swallowed. What it actually does is suppress the heart and brain, as described above. People who have spiked drinks with eyedrops expecting a harmless joke have instead caused hospitalizations and, in some cases, death.

The forensic literature includes cases where eyedrops were used as a deliberate poison. The atropine case mentioned earlier, in which two bottles of prescription atropine drops were emptied into a victim’s beer, ended in a homicide conviction.⁴ In the United States, a widely reported 2018 case involved a woman who was convicted of murder after repeatedly putting Visine drops into her husband’s water over a period of days. These cases underscore that the consequences are real and that law enforcement and toxicologists take eyedrop poisoning seriously. Screening for imidazoline compounds is now part of standard forensic toxicology panels in many jurisdictions precisely because of these incidents.

What to Do If Someone Swallows Eyedrops

If you suspect that a child or adult has swallowed eyedrops containing tetrahydrozoline, brimonidine, or any other active medication, the first step is to call poison control (1-800-222-1222 in the United States) or emergency services immediately. Do not try to induce vomiting unless specifically instructed to by a poison control specialist, as the sedation caused by the drug can increase the risk of choking.

In the hospital, treatment is mainly supportive. Medical teams monitor heart rate, blood pressure, oxygen levels, and level of consciousness. Intravenous fluids can help stabilize blood pressure. If the heart rate drops too low, medications like atropine (somewhat ironically, the same drug that is toxic in its own right at high doses) may be given to speed it back up. In severe cases, temporary cardiac pacing can be used to maintain a safe heart rhythm until the drug clears the body.

For brimonidine specifically, veterinary toxicology literature suggests that alpha-2 antagonists like yohimbine and atipamezole can reverse the drug’s effects.⁵ These reversal agents are less commonly used in human medicine, but the principle of receptor-level reversal is the same, and poison control centers are aware of the option for critical cases.

Recovery depends heavily on the amount ingested, the person’s age and overall health, and how quickly treatment begins. Most adults who receive prompt care after a moderate ingestion recover fully, though cardiac monitoring may continue for 24 hours or more because the heart rhythm disturbances can persist after other symptoms have improved.¹ The elderly man in the published case report, despite ingesting a very large amount, survived with medical management, though his ECG abnormalities took time to resolve.

How Even Normal Use Can Send Drugs Into the Bloodstream

An interesting wrinkle in eyedrop pharmacology is that even normal, intended use on the eye sends some of the drug into the body. When you put a drop in your eye, much of the liquid drains through the nasolacrimal duct, the tiny channel that connects the inner corner of the eye to the nose and throat. From there, the drug can be absorbed through the nasal mucosa or swallowed and absorbed through the gut. A review of the literature found that techniques like pressing on the inner corner of the eye after instilling a drop, or simply keeping the eyes closed for a couple of minutes, reduce this systemic absorption and improve how much drug actually reaches the eye.⁶

For most healthy adults using redness-relief drops as directed, this trickle of systemic absorption is too small to cause problems. But for people on glaucoma medications like timolol (a beta-blocker in eyedrop form) or brimonidine, the cumulative systemic exposure from daily use can occasionally produce side effects like a slow heart rate or low blood pressure, especially in smaller or older patients. This is one reason ophthalmologists sometimes recommend the press-and-close technique: it keeps more of the drug in the eye and less in the bloodstream.

The clinical lesson is that eyedrops are real medications with real systemic pharmacology, not inert cosmetic products. The casual attitude many people have toward eyedrops, leaving them on nightstands within toddler reach, never reading the label, assuming they are harmless if swallowed, reflects a broader misunderstanding. A 15 mL bottle of Visine contains a drug potent enough to alter heart conduction, suppress consciousness, and, in the worst cases, kill. Treating it with the same respect you would give any other over-the-counter medication is not excessive. It is appropriate.

Pets and Eyedrop Ingestion

Dogs and cats are also at risk, and veterinary poison hotlines report eyedrop ingestion as a recurring problem. Dogs in particular tend to chew on small plastic bottles, potentially swallowing the contents. A study of 52 dogs that accidentally ingested brimonidine eyedrops documented bradycardia in about two-thirds of cases, along with depression, low blood pressure, weakness, and hypothermia.⁵ Shock, weak pulses, and poor capillary refill were also reported in some animals. Treatment included early decontamination, supportive care, and in some cases the use of alpha-2 antagonists to reverse the drug’s cardiovascular effects.

Tetrahydrozoline poses similar risks to pets. A small dog that chews through a bottle of Visine faces proportionally the same danger as a toddler who swallows the liquid. If you suspect your pet has gotten into eyedrops, contact your veterinarian or an animal poison control service without waiting for symptoms to appear. The cardiovascular effects can develop rapidly, and early intervention makes a significant difference in outcome.