Dr Shu Lin, Dr Yan-Chuan Shi and Professor Herbert Herzog, from Sydney's Garvan Institute of Medical Research, have shown that when mice are injected with PYY3-36 and PP, they eat less, gain less fat, and tend not to develop insulin-resistance, a precursor to diabetes. At the same time, the researchers have shown that the hormones stimulate different nerve pathways, ultimately, however, affecting complementary brain regions. Their findings are now published online in the journal Obesity.

While the double-barreled approach may seem like a no-brainer, the strongly enhanced effect seen was by no means inevitable. In the complex world of neuroscience, two plus two does not always make four.

Drug companies are in the process of conducting pre-clinical trials to examine the separate effects of boosting the hormones PYY3-36 and PP. Until now, there is no research to indicate the detailed molecular interactions that might occur when they are boosted in tandem.

When used together, the hormones independently, yet with combined force, reduce the amount of neuropeptide Y (NPY) produced by the brain, a powerful neurotransmitter that affects a variety of things including appetite, mood, heart rate, temperature and energy levels.

Each hormone also communicates with a different part of the arcuate nucleus in the hypothalamus, a region of the brain where signals can cross the normally impermeable blood / brain barrier. The stimulated regions then produce other neuronal signals deep within the hypothalamus, bringing about a powerful combined effect.

"There are many factors that influence appetite control -- and we now realise that there won't be a single molecular target, or a single drug, that will be effective," said Dr Yan-Chuan Shi.

"It will be important for drug companies to try different combinations of targets, to see which combinations are most potent, and at the same time have no side effects, or at least minimal side effects."

"At the moment, the only effective tool against obesity is surgery. Drug companies have so far failed to produce an effective drug without unacceptable side effects, such as mood disorders, nausea or cardiovascular problems."