Just taken my supplements again and they're already kicking in! I'm not talking fast as in hours, I'm talking minutes and the B12 is a handful of seconds!
If you're feeling grotty then ask your GP to test your vitamin levels and take it from there!
I've always taken supplements to help my body along a bit but didn't really see much difference before I found out my B12 levels were so low... I've added a B complex and vitamin B12 to my list of supplements and I'm also taking vitamin C to help my immune system as well as Calcium because I'm allergic to dairy and my standard multivitamin and I see the world in HD within minutes of taking them instead of grainy black and white when I don't!
They really do work for me!