Are Monitor lizards venomous

dont know the reason, but under some stress, or conditions where my varanus acanthurus has had to be defensive and ready, he(the male) has simulated vomitting. He will shake his head left and right and release(sometimes fling) almost whole crickets out of his mouth. There are some hissing, exhaling sounds, and jerky movements. afterwards he seems fine, and resumes eating successfully the following day.