I never had any luck with it and I am not impressed with some of the low dosages of active ingredients. 30 iu of synthetic vit E is not worth squat nor is the 40mg of magnesium. 8 mg of zinc is only half of the RDA which we all know is way too low for most nutrients.
There is far more research on black elderberry and whole plant echinacea. I have had perfect results with taking high doses of both when I feel a bug comming on. Just last week I got a scratchy throat and swollen lymph glands and within 24 hrs I knocked it out. It's been three years since I have had any colds or flu and I work in a enclosed room with many people every day. I also nasal irrigate with saline and colloidal silver year round.
But if it works for you then don't stop, there are no side effects and you don't need to screw around with doc visits and prescriptions to use it. The same is true for homeopathic remedies.