When I was a kid, I used to feed stray kittens. My parents would not let me bring any of them to the vet. 
There was this sweet kitten who had a swollen belly and one day I saw a white ascarid worm halfway out of his butt. I couldn't give him meds and I was not allowed to bring him to the vet. So the only thing I could do was to feed him loads of garlic. After around a week on garlic and minced meat he did not have any visible symptoms of worms. No swollen belly, clean fur, no funny spagetti crawling out of his bum. 
Plants might not be the best medicine, but it's certainly better than nothing. Most of our medicines are synthetized from plant after all.