When deciding whether to approve a drug, the FDA only cares whether it's safe and effective. But once the drug hits the market, a third characteristic -- how the drug is taken -- helps determine whether it obtains blockbuster status.

Most type 2 diabetes patients have started out on oral medications like Bristol-Myers Squibb's (NYSE:BMY) Glucophage -- available as generic metformin -- then progressed to injectable insulin. Newer medications like Merck's (NYSE:MRK) Januvia sought to put off the inevitable needle pokes by giving patients another oral therapy before heading on to insulin.

Then there's Amylin Pharmaceuticals' (NASDAQ:AMLN) Byetta. An analog of the hormone GLP-1, this wonder drug improves glucose levels and helps diabetics shed pounds -- but it has one big problem. Byetta aims to help patients avoid using insulin, but still results in two needle pokes a day, which has put a damper on its sales. Novo Nordisk (NYSE:NVO) has tried to best Byetta by developing a competing GLP-1 analog that only needs to be injected once a day.

If one injection a day is better than two, then one injection per week should be seven times better. That's what Amylin and marketing partner Eli Lilly (NYSE:LLY) are doing with Byetta. Using Alkermes' (NASDAQ:ALKS) microsphere technology, the once-weekly Byetta looked good in trials, although it's still more than a year away from being on the market.

Novo Nordisk isn't waiting idly by to be outdone by once-weekly Byetta, though. The diabetes expert announced yesterday that it's taking drug delivery full circle by attempting to make an oral version of GLP-1-like drugs. It won't be easy; if it were, Amylin, Novo Nordisk, and others would have started there in the first place. But Novo Nordisk thinks it can use Emisphere Technologies' (NASDAQ:EMIS) eligen technology to carry GLP-1 drugs across the membranes of the gut and into the bloodstream.

Hold on to your seat, Fools. The GLP-1 drug wars are going to deliver one bumpy ride.