Acetylcysteine

Many people know acetylcysteine, also called N-acetylcysteine or NAC for short, as a cough medicine from the pharmacy. In veterinary medicine the drug has two jobs. It thins sticky mucus in the airways, and it serves as an antidote in paracetamol poisoning.

Emergency: If your dog has eaten paracetamol or another painkiller meant for humans, call your vet or an emergency vet service immediately. How your dog fares afterwards depends on the amount and on how quickly treatment starts. Do not give home remedies or acetylcysteine from your own medicine cabinet.

According to CliniPharm (University of Zurich), no veterinary medicine containing acetylcysteine is currently licensed in Switzerland. In Germany and Austria, eye drops containing acetylcysteine are licensed as a veterinary medicine for dogs and cats. We are not aware of any oral or injectable product licensed for dogs. If no suitable veterinary medicine is available, the vet decides case by case whether to use a product for humans. This is called off-label use (known as cascade use in Europe), and it is reserved for vets.

What is acetylcysteine used for in dogs?

Paracetamol poisoning: This is the drug’s most important role. In dogs, paracetamol can damage mainly the liver and, in large amounts, also the red blood cells. Cats are considerably more sensitive still. Acetylcysteine is regarded as the antidote. If treatment starts early, it can help reduce damage to the liver and blood.

Airways: In conditions with sticky mucus in the bronchi, acetylcysteine can thin the mucus so the dog can cough it up more easily. In dogs there are only a few studies on this, mostly experimental. It has not been shown to work in sick dogs.

Liver and other poisonings: Some vets also use acetylcysteine for liver disease or other poisonings, because it acts as an antioxidant. The evidence for this is still preliminary (Tóth et al., 2026; Mahendra et al., 2026). Whether it makes sense for an individual dog is decided by the vet.

How does acetylcysteine work?

Mucus-thinning: Acetylcysteine breaks certain bonds in the mucus, the disulphide bridges. This makes sticky mucus more runny.

Detoxifying: When paracetamol is broken down, toxic substances are produced. The body neutralises them with glutathione, as long as there is enough of it. Acetylcysteine supplies a building block from which the body makes new glutathione.

Dosage and form

The dose is always set by the vet. It depends on what acetylcysteine is being used for, and on the dog’s weight and condition.

Depending on the purpose, the dog receives acetylcysteine by mouth, as an infusion into a vein, by inhalation through a nebuliser or as eye drops. Poisoning is treated at the practice, not at home.

Side effects and precautions

Nebulising: When inhaled, acetylcysteine can cause a reflex narrowing of the bronchi. It is therefore recommended to give a medicine that widens the bronchi beforehand.

Watch for: If your dog vomits after a dose, if its skin itches or turns red, if anything swells up or if it breathes more heavily, contact your vet immediately.

Tell the vet which other medicines your dog is taking and whether your bitch is pregnant or nursing.