It doesn't. Or, I should say, rarely. Like with just about anything, one can get what they call a paradoxical reaction (ie. the opposite of expected), but it is not typical.

Lamictal is considered most effective on the depressive side of things. Dosages vary pretty widely -- as with anything, if your dose if effective for you, that's great, Ohlala, and no point in changing what is working! I've been put as high as 400mg on it. (Me: far more depression-prone and have gone at various levels between 200mg and 400mg.)

When all is said and done, we're all different in reactions and dosages, what works and what doesn't or what works for a time. Keeps the fun in the med-go-round. (Yeah, right! That'd be sarcasm... )