Ivermectin toxicity in cats typically lasts days to weeks, depending on the dose ingested and how quickly treatment begins. Mild cases may resolve within a few days, while severe poisoning can require weeks of intensive supportive care before a cat fully recovers. Blindness, one of the most alarming symptoms, generally reverses within 2 to 8 days, though the exact timeline varies.
Why Cats Are Vulnerable to Ivermectin
Ivermectin works by overstimulating certain receptors in the nervous system of parasites, paralyzing and killing them. In mammals, the brain is normally protected from this effect by a protein called P-glycoprotein, which acts like a gatekeeper at the blood-brain barrier, pumping the drug back out before it can reach brain tissue. Cats have less of this protective transporter activity than some other species, which makes them more susceptible to toxicity even at relatively low doses.
Some cats carry a specific genetic mutation in the MDR1 gene (the gene responsible for producing P-glycoprotein) that makes the problem far worse. A two-base-pair deletion in this gene has been identified in cats, particularly Maine Coons, that essentially disables the blood-brain barrier’s ability to keep ivermectin out. Cats homozygous for this mutation, meaning they inherited a copy from both parents, are especially sensitive and can develop severe neurological signs at doses other cats might tolerate. There is no widely available screening test for this mutation in cats the way there is for certain dog breeds, so the risk is often discovered only after a toxic reaction occurs.
How Quickly Symptoms Appear
Signs of ivermectin toxicity usually develop within 1 to 12 hours after exposure. In one documented case involving a kitten, mild tremors, weakness, incoordination, and constricted pupils appeared within 6 hours. By 12 hours, the kitten was lying on its side and completely unresponsive. The speed and severity of onset depend heavily on the dose. Kittens given 0.4 mg/kg in research settings developed dilated pupils, unsteady movement, and heightened sensitivity to touch within 12 hours. At 1 mg/kg, some kittens deteriorated into coma.
What Ivermectin Toxicity Looks Like
The symptoms are primarily neurological because the drug is crossing into the brain and amplifying signals that normally inhibit nerve activity. When ivermectin reaches the brain, it locks onto receptors that control how “quiet” neurons stay, essentially turning the volume up on the brain’s own calming signals until the nervous system becomes dangerously suppressed.
Common signs include:
- Tremors and muscle twitching, often among the first symptoms noticed
- Unsteady walking (ataxia), progressing to inability to stand
- Dilated pupils and blindness, with no response to visual threats or light
- Depression and lethargy, ranging from sluggishness to complete unresponsiveness
- Coma in severe cases, where the cat cannot be roused
- Diarrhea and loss of appetite, particularly at higher doses
In a case involving five cats from the same household who were accidentally exposed, all five presented with sudden tremors, dulled awareness, blindness, and dilated pupils that did not react to light. This cluster pattern is worth noting: if multiple cats in a home show sudden neurological signs simultaneously, shared exposure to a toxin like ivermectin should be high on the list of possibilities.
How Long Recovery Takes
There is no single answer because the timeline depends on dose, body weight, genetic sensitivity, and whether treatment was started early. That said, veterinary literature provides useful ranges.
For mild to moderate cases, where the cat is still conscious but showing tremors, unsteadiness, or visual changes, symptoms often begin improving within a few days with supportive care. Blindness specifically tends to be temporary, with vision returning in roughly 2 to 8 days in most documented cases.
Severe cases tell a different story. Cats that become comatose or completely unresponsive may need intensive care for weeks. In one treatment study, severely intoxicated cats required ongoing therapy for 72 to 168 hours (3 to 7 days) before clinical signs resolved, and that timeframe reflects only the acute crisis, not necessarily a return to completely normal function. Full neurological recovery after severe poisoning can stretch beyond that, with lingering unsteadiness or visual deficits gradually resolving over the following weeks.
Body condition plays a role too. Ivermectin is highly fat-soluble, which means it accumulates in body fat and is released slowly. Cats with low body fat may experience a more intense but shorter course, while the drug can linger longer in cats with more fat stores. However, thinner cats were also found to be more likely to develop clinical signs and to require more treatment overall, likely because less body fat means a higher concentration of the drug reaching the brain quickly.
What Treatment Involves
There is no antidote for ivermectin toxicity. Treatment is primarily supportive, meaning the veterinary team keeps the cat alive and stable while the drug is gradually cleared from the body.
One treatment that has shown real promise is intravenous lipid emulsion therapy. Because ivermectin is fat-soluble, infusing a fat-based solution into the bloodstream can essentially “soak up” the drug, pulling it out of brain tissue and trapping it in the fat droplets circulating in the blood. In a study of cats treated this way, those who received an initial dose followed by a sustained infusion fared better than those who received only a single dose. Cats with moderate toxicity needed treatment for about 36 hours on average, while severely affected cats required it for roughly 96 hours.
Beyond lipid therapy, supportive care includes intravenous fluids to maintain hydration, temperature regulation (comatose cats cannot regulate their own body heat), nutritional support for cats that cannot eat, and careful monitoring of heart rate and breathing. Cats in a coma need to be repositioned regularly to prevent pressure sores and lung complications from lying in one position.
What to Expect During Recovery
Recovery from ivermectin toxicity is not a sudden event. It tends to happen in stages. A comatose cat may first begin showing intermittent signs of awareness, such as blinking or slight head movements, before becoming more consistently responsive. Motor coordination usually returns before vision does, so you may see your cat able to stand and walk unsteadily while still appearing blind.
Vision recovery deserves special attention because it causes the most anxiety for cat owners. The blindness is caused by the drug’s effect on the nervous system, not by permanent damage to the eyes themselves. In the vast majority of documented cases, vision returns once the drug clears. The 2 to 8 day window is the most commonly cited range, but some cats take longer, and there is limited data on whether a small percentage experience lasting visual impairment.
Cats that survive the acute phase generally make a full recovery. The key factors that determine outcome are the dose of ivermectin involved, how quickly veterinary care begins, and whether the cat has the MDR1 genetic mutation that impairs drug clearance. Young kittens and underweight cats are at higher risk for severe outcomes because of their smaller body mass and lower fat reserves.