Can I give my Shih Tzu human vitamins and brewers yeast?

by Angel Fernando
(Philippines)

At what age is it alright to give a shih tzu BREWER'S YEAST? and how often should it be given?

How about multivitamins? I read some articles on the internet, they give infant(human) multivitamins or vitamin C. Is it alright? Does it have any side effects to the dogs?