The ratings of seven biotechnology stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Genomic Health, Inc.’s (GHDX) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. 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. In Portfolio Grader’s specific subcategory of Earnings Revisions, GHDX also gets an F. To get an in-depth look at GHDX, get Portfolio Grader’s complete analysis of GHDX stock.

This is a rough week for Acorda Therapeutics, Inc. (ACOR). The company’s rating falls to D from the previous week’s C. 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 a full analysis of ACOR stock, visit Portfolio Grader.

The rating of Amarin Corporation Plc Sponsored ADR (AMRN) slips from a C to a D. Amarin focuses on developing the treatment for cardiovascular disease in the field of lipid science. In Earnings Growth, Earnings Revisions, Equity and Cash Flow the stock gets F’s. As of Dec. 11, 2013, 18.8% of outstanding Amarin Corporation Plc Sponsored ADR shares were held short. For more information, get Portfolio Grader’s complete analysis of AMRN stock.

Exelixis, Inc.’s (EXEL) rating falls this week to an F (“strong sell”), down from last week’s 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 gets F’s in Earnings Growth, Earnings Momentum and Equity. Margin Growth and Sales Growth also get F’s. As of Dec. 11, 2013, 25.2% of outstanding Exelixis, Inc. shares were held short. For a full analysis of EXEL stock, visit Portfolio Grader.

Slipping from a C to a D rating, Trius Therapeutics, Inc. (TSRX) takes a hit this week. Trius Therapeutics is a biopharmaceutical company. The stock receives F’s in Earnings Growth, Earnings Momentum and Equity. Cash Flow and Sales Growth also get F’s. To get an in-depth look at TSRX, get Portfolio Grader’s complete analysis of TSRX stock.

Discovery Laboratories, Inc. (DSCO) gets weaker ratings this week as last week’s C drops 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. For more information, get Portfolio Grader’s complete analysis of DSCO stock.

Achillion Pharmaceuticals, Inc. (ACHN) earns a D this week, moving down from last week’s grade of C. Achillion focuses on the discovery, development and commercialization of innovative treatments for infectious diseases. The stock also gets an F in Equity. As of Dec. 11, 2013, 18.5% 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.