Clinical trials have shown that, after injection, no signs of pain were apparent. Immediate or delayed swelling may be found at the injection site. On rare occasions (approx 1%), these swellings may further develop into abscesses. The frequency of injection site swellings tends to be higher in the heavier animals. The side effects generally disappear, without treatment, within 14 days of administration, some may persist for up to 5 weeks in a number of animals (<5%) and in very rare occasions longer.

Signs of overdose are consistent with the mode of action of moxidectin. These signs are manifested as transient salivation, depression, drowsiness and ataxia 24 to 36 hours post-treatment. The signs usually disappear within 36 to 72 hours without treatment. At doses >3 times the recommended dose, the signs include recumbency, muscle tremor, ruminal tympany and dehydration. The signs can last for a few days to ten days. There is no specific antidote.

On rare occasions, depression and ataxia can be observed after injection. Cydectin 10% LA for Cattle has been shown to be safe for use in pregnant animals.

Immunity to nematodes depends on adequate exposure to infection. Although not normally the case, circumstances could occur in which anthelmintic control measures might increase the vulnerability of cattle to re-infection. Animals may be at risk towards the end of their first grazing season, particularly if the season is long, or in the following year if they move onto heavily contaminated pasture. In such instances, further control measures may be necessary.