In the topsy-turvy world of health care, some stocks get rocked the most. Here is a look at three of the health-care stocks with the most horrendous performance for the week.

Super news?
Supernus Pharmaceuticals (SUPN -0.45%) actually received good news this week, but you wouldn't know it from the way the stock performed. Shares dropped over 23% during the week.

The good news stemmed from FDA approval of Oxtellar XR for use in the treatment of epilepsy. This marked the second FDA nod for Supernus after it went public in May this year. The company received tentative approval for another epilepsy drug, Trokendi XR, in June.

Why the large decline on good news? Profit-taking could have driven shares down to some degree. The stock is very thinly traded, though, so any number of other factors could have been at work.

Loss leader
A week that started off with a slow downward path ended with a steep drop for Immunogen (IMGN). Shares fell 21% on the week. Investors seem to have been expecting bad news with the company's quarterly results. And bad news is what they got. 

The company reported its fiscal first quarter results on Friday. Losses topped $25 million. That's 29% worse than the same quarter last year. While Immunogen reported $1.6 million more in revenue compared to last year, operating expenses grew at a faster pace, rising $7.3 million during the quarter versus 2011. Research and development costs surged nearly 40%.

Immunogen looks to approval of its cancer drug T-DM1, which is being developed in partnership with Roche, as the catalyst to improve the company's fortunes. Roche has a study in progress with T-DM1 for second-line treatment of metastatic HER2+ gastric cancer. The company expects to file for marketing approval in 2015.

Fat chance
VIVUS (VVUS) rounds out our list of horrendous performers for the week. Shares fell nearly 15%.

The company received notification on Oct. 18 that the European Medicines Agency's Committee for Medicinal Products for Human Use rejected marketing approval for obesity drug Qsymia. The stock has steadily declined since the announcement.

You might think that this bad news for VIVUS would benefit rivals Arena Pharmaceuticals (ARNA) and Orexigen Therapeutics (NASDAQ: OREX). That didn't happen this week, though.

Arena fell around 8% during the week. Orexigen dropped even more -- around 10%. Orexigen could be positioned to do well, though. Fool analyst David Williamson thinks that Orexigen could present a major threat to both other competitors down the road.

Best of the worst
My pick as the best of the worst for this week is Immunogen. Supernus doesn't trade broadly enough. Things don't look great for VIVUS, with the European decision and two significant  competitors. 

Immunogen, though, could see brighter days ahead. The company has plenty of cash to take it well into the future. It has solid partnerships in place, and several promising drugs in the pipeline. You could definitely do worse than going with Immunogen.