Peter, Peter, Peter, your not sure it has stopped the behaviour much??? For who, you or the kid???

Time out, Time out, Time out, BEFORE it escalates, practice the Time Out method on the offending child to a dedicated "Naughty Spot" and firmly(not loudly) explain to them that biting another person is not acceptable, "we are people not food".

I think the rule is one minute per year of age. ie. 2 years old = 2 minutes

Good luck

I'm pretty sure it's a stage. A quick google on biting comes up with a number of sites, so it's pretty common.

It specifically states to resist the urge to bite back. I did... and hard too. Through the cries and wailing I said " did you like that? did you like that? ".
He never bit ME again, but I'm not sure it stopped the behaviour much *sigh*.

Anyways, I have included a link you may want to have a look at.

Stopping Toddler Biting Behaviours

Ignore bad behaviour. Like so many other forms of bad behaviour, in my experience active ignorance is the best medicine. An 18-month old isn't really capable of deep reasoning, but they do understand that when they bite, they get lots of attention, not only from the victim, but from the surrounding adults.

I'd remove the offending child to a quiet place for time-out, very calmly explain to him that we bite food, not people, and give him about 90 seconds of time-out. It's really important not to actively tell him off, as that's just extra attention, and at 18 months they need to know that your love is unconditional.

Can you sense when the circumstances in which biting is likely to occur are about to happen? You mentioned tiredness, hunger is also an obvious one. It might be possible to head this behaviour off at the pass by providing good teething food before the biting starts, eg carrots, rusks, etc - but don't reward biting with food! If hunger isn't an issue and things look like they're about to seriously deteriorate into biting mode, maybe it's time for a quiet story or similar activity.

Hope this helps.