The risk-benefit analysis for drugs can be one of the trickiest things for investors to determine. Unfortunately documents published ahead of Bristol-Myers Squibb's (NYSE: BMY) Food and Drug Administration advisory panel on Monday don't clear things up much.

The advantages of Bristol-Myers' potential kidney transplant drug, belatacept, are clear. According to Bristol-Myers, belatacept doesn't have the toxicity seen in Abbott Labs' (NYSE: ABT) Gengraf and Novartis' (NYSE: NVS) Sandimmune and Neoral. The FDA noted that more patients were alive two years after taking belatacept compared to the older medications.

But -- and there's always a but -- the drug isn't perfect. There were some complications with kidney rejections in some patients and cases of progressive multifocal leukoencephalopathy (PML) were also observed.

The risk of PML is always a concern for drugs that suppress the immune system because PML is caused by a viral infection. For some drugs, like Biogen Idec's (Nasdaq: BIIB) and Elan's (NYSE: ELN) Tysabri, the rewards of the drug are seen as justifying the risk. For others, like Genentech's Raptiva, they aren't.

We won't know which side of the question belatacept falls on until the committee votes Monday. Quantifying whether the benefits outweigh the risks is difficult enough for transplant doctors let alone those of us with far less experience.

Based on the FDA documents, I'd guess belatacept has a good chance of getting past the committee, but it's not a slam dunk. The agency doesn't have to follow the panel's advice, but given the complex nature of risk/benefit analysis, I expect the experts vote will weigh heavily when the agency makes its final decision on or around May 1.

Sit tight investors, there isn't much longer to wait.

Here are a few more drugmakers expecting FDA decisions this year.