What are the differences between grehlin and leptin?

Satiation vs hunger: Leptin is for satiation vs ghrelin for hunger. Leptin is a mediator of long-term regulation of energy balance, suppressing food intake and thereby inducing weight loss. Ghrelin on the other hand is a fast-acting hormone, seemingly playing a role in meal initiation.

The yin/yang of diet: Gherlin, a peptide secreted by the fundus of the stomach, increases before meals and falls after meals; whereas leptin, produced by adipose cells, interacts with the cns, specifically neuropeptide y in the arcuate nucleus wherein it induces satiety, or a sense of fullness. Currently, intense research exists to temper obesity via a pill and diet, rather than, say, gastric bypass.