thanks so much both of you; that's reassuring. That's a very useful link too! So far he's fine (touch wood and all IKEA variants thereof lol) and in fact has had a good nosh. Reading it, I can see why Vitamin B has made a difference to his behaviour (bit less subdued, has even played a wee bit) and his coat's been really silky. Actually I'd recommend it as a supplement to anyone whose cat is elderly and a bit weak or not too active. It's also supposed to help with any neuro damage (a bit).
Obviously not in overdose by dumb-mums though!! It's ironic really as he takes 'my' vitamins and I never remember to take them myself!
Don't think I'll give him another for 2-3 days though.
If I don't write things down, I just forget