The overall ratings of eight biotechnology stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

TESARO, Inc. (TSRO) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. For Portfolio Grader’s specific subcategory of Equity, TSRO also gets an F. The stock price has dropped 7.5% over the past month, worse than the 1.3% decrease the Nasdaq has seen over the same period of time. For a full analysis of TSRO stock, visit Portfolio Grader.

The rating of Genomic Health, Inc. (GHDX) slips from a C to a D. Genomic Health is a life science company, which is focused on the development and commercialization of genomic-based clinical diagnostic tests for cancer that allow physicians and patients to make individualized treatment decisions. The stock also gets an F in Earnings Revisions. To get an in-depth look at GHDX, get Portfolio Grader’s complete analysis of GHDX stock.

Acorda Therapeutics, Inc. (ACOR) is having a tough week. The company’s rating falls from a C to a D. Acorda Therapeutics is a commercial stage biopharmaceutical company dedicated to the identification, development and commercialization of novel therapies that improve neurological function in people with multiple sclerosis (MS), spinal cord injury and other disorders of the central nervous system. The stock gets F’s in Earnings Revisions and Sales Growth. For more information, get Portfolio Grader’s complete analysis of ACOR stock.

This week, Amarin Corporation Plc Sponsored ADR’s (AMRN) rating worsens to a D from the company’s C rating a week ago. Amarin focuses on developing the treatment for cardiovascular disease in the field of lipid science. The stock gets F’s in Earnings Growth, Earnings Revisions, Equity, and Cash Flow. As of Nov. 19, 2013, 18.9% of outstanding Amarin Corporation Plc Sponsored ADR shares were held short. Shares of the stock have been changing hands at an unusually rapid pace, up 592.7% from the week prior. To get an in-depth look at AMRN, get Portfolio Grader’s complete analysis of AMRN stock.

Exelixis, Inc. (EXEL) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Exelixisis a development-stage biotechnology company dedicated to the discovery and development of small-molecule therapeutics for the treatment of cancer and other serious diseases. The stock receives F’s in Earnings Growth, Earnings Momentum, and Equity. Margin Growth and Sales Growth also get F’s. As of Nov. 19, 2013, 25.8% of outstanding Exelixis, Inc. shares were held short. For more information, get Portfolio Grader’s complete analysis of EXEL stock.

Trius Therapeutics, Inc.’s (TSRX) rating weakens this week, dropping to a D versus last week’s C. Trius Therapeutics is a biopharmaceutical company. The stock gets F’s in Earnings Growth, Earnings Momentum, and Equity. Cash Flow and Sales Growth also get F’s. For a full analysis of TSRX stock, visit Portfolio Grader.

Discovery Laboratories, Inc. (DSCO) experiences a ratings drop this week, going from last week’s C to a D. Discovery Laboratories is a biotechnology company focused on developing products for the treatment of respiratory disease. The stock gets F’s in Equity and Cash Flow. To get an in-depth look at DSCO, get Portfolio Grader’s complete analysis of DSCO stock.

Slipping from a C to a D rating, Achillion Pharmaceuticals, Inc. (ACHN) takes a hit this week. Achillion focuses on the discovery, development and commercialization of innovative treatments for infectious diseases. The stock also rates an F in Equity. At $2.55, the stock is below the 50-day moving average of $3.96. As of Nov. 19, 2013, 19.8% of outstanding Achillion Pharmaceuticals, Inc. shares were held short. For a full analysis of ACHN stock, visit Portfolio Grader.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.