Zaditor is an over-the-counter eye drop used to prevent and relieve itchy eyes caused by allergies. Its active ingredient, ketotifen fumarate, works in two ways: it blocks histamine (the chemical your body releases during an allergic reaction) and it stabilizes the cells that release histamine in the first place. This dual action makes it one of the more effective options on the pharmacy shelf for seasonal and environmental eye allergies.
What Zaditor Treats
Zaditor is FDA-approved specifically for the temporary prevention of itching of the eye due to allergic conjunctivitis. That’s the medical term for the red, itchy, watery eyes you get from pollen, pet dander, dust mites, mold, or other airborne allergens. It targets itching as its primary symptom, though many people notice improvement in redness and watering as well since those symptoms share the same underlying allergic response.
Zaditor is not designed to treat eye infections, dry eye, or irritation from contact lenses. If your eyes are itchy but you don’t have allergies, a different type of drop is likely a better fit.
How It Works
Most allergy eye drops do one thing: block histamine after it’s already been released. Zaditor does that, but it also prevents the release of histamine from mast cells, which are immune cells in your eye tissue that trigger the allergic cascade. By working on both sides of the reaction, ketotifen can both treat symptoms that are already happening and help prevent them from starting if you use it before exposure.
This is why Zaditor can be useful as a preventive measure. If you know you’re heading into a high-pollen day or visiting a home with pets, applying a drop before exposure gives the mast cell stabilizing effect time to kick in.
How Fast It Works and How Long It Lasts
In FDA clinical trials, Zaditor showed an onset of action at about 15 minutes after application. Relief from itching lasted up to 8 hours per dose, confirmed through allergen challenge tests at both 6 and 8 hours. That timeline lines up well with a twice-daily dosing schedule, covering most of the waking day with two applications.
Dosage and How to Apply It
The standard dose is one drop in each affected eye, twice daily, spaced 8 to 12 hours apart. It’s approved for adults and children ages 3 and older. You should not exceed two doses in a 24-hour period.
To get the most out of each drop, tilt your head back slightly, pull down your lower eyelid to create a small pocket, and place the drop there. Try not to touch the tip of the bottle to your eye or any surface, as this can introduce bacteria. After applying, close your eye gently for a moment rather than blinking rapidly, which can push the drop out before it absorbs.
Contact Lens Guidelines
If you wear soft contact lenses, remove them before applying Zaditor. The drops contain a preservative called benzalkonium chloride, which can be absorbed by soft lens material and irritate your eyes over time. Wait at least 10 minutes after applying the drops before reinserting your lenses. This gives the solution enough time to absorb and clears the preservative from your eye’s surface.
If you use other eye medications alongside Zaditor, space them at least 5 minutes apart to prevent one drop from washing out the other.
Side Effects
The most common side effect is a temporary burning or stinging sensation right after you put the drop in. In one clinical trial, 98% of the 35 participants reported some degree of burning or stinging, though it was rated as mild to moderate and typically fades within a minute or two. Other reported side effects occurring in 1% to 10% of users include eye irritation, eye pain, and minor surface changes to the cornea (tiny dot-like erosions that generally resolve on their own).
Serious side effects are rare. If you experience significant eye pain, vision changes, or worsening redness after using Zaditor, stop using it and have your eyes evaluated.
Who Should Avoid Zaditor
The only formal contraindication is a known allergy to ketotifen or any of the inactive ingredients in the solution. There are no well-studied drug interactions with other medications when used as eye drops, since very little of the active ingredient reaches the bloodstream.
Safety data in pregnant or nursing women is limited. No clinical trials have been conducted in these groups, so the general recommendation is to weigh the benefit against the unknown risk.
Storage
Store Zaditor between 39°F and 77°F (4°C to 25°C). That means room temperature is fine for most homes, but avoid leaving the bottle in a hot car or in direct sunlight. The product label does not specify a discard date for opened bottles, but a good rule of thumb for preservative-containing eye drops is to replace them after the expiration date printed on the packaging or if the solution looks cloudy or discolored.