The short interest data are out for the December 31 settlement date. Biotech companies are considered a riskier group of stocks, with big upside and big downside. FDA rulings can make or break them. A single failed clinical trial can mean disaster for a stock. 24/7 Wall St. has reviewed the top biotech companies, without focusing on speculative companies.

The December 31 short interest data have been compared with the December 15 figures, and for the majority of the selected stocks, short interest is down.

Amgen Inc. (NASDAQ: AMGN) saw its short interest rise to 8.04 million shares with 2.2 days to cover. The previous short interest reading was 7.86 million with 2.4 days to cover. The short interest for Amgen has taken a dip for these past two settlement dates, recording the lowest levels on the year. Shares closed Monday at $156.22, in a 52-week trading range of $108.20 to $173.14.

Biogen Idec Inc. (NASDAQ: BIIB) saw its short interest rise to 2.90 million with 1.6 days to cover from the last level of 2.85 million shares with 1.3 days to cover. The company is coming off its lowest short interest readings in November and seemingly returning to its recent historic levels. Shares closed Monday at $347.84, within a 52-week trading range of $272.02 to $361.93.

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Celgene Corp. (NASDAQ: CELG) short interest back off slightly for this settlement date, down to 10.04 million shares with 1.4 days to cover. The level for the previous settlement date was 10.37 million with 2.2 days to cover. Since March, Celgene has recorded its two lowest relative readings in the past two settlement dates. This is potentially signaling some optimism from investors. Shares of Celgene closed Monday at $117.00, in a 52-week trading range of $66.85 to $119.84. Celgene just gave its earnings outlook to 2020.

Gilead Sciences Inc. (NASDAQ: GILD) saw its short interest fall to 52.9 million with two days to cover from 55.5 million with four days to cover. Investors seem to have relatively backed off shorting this stock in September, when shares were poised to hit 52-week highs just a month later after the market sell-off, which surprisingly only had a relatively small increase for short interest in that period. Shares closed Monday at $101.21, in a 52-week trading range of $63.50 to $116.83.

Mannkind Corp. (NASDAQ: MNKD) saw its short interest fall to 75.7 million shares with 18.1 days to cover. The previous reading for short interest was 78.8 million with 20.1 days to cover. Short interest for Mannkind appears to have steadily backed off from its 52-week highs following the market sell-off In October. Shares closed Monday at $8.93, in a 52-week trading range of $3.80 to $11.48.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest increased to 2.93 million shares with 2.2 days to cover, up from the last level of 2.71 million with 2.5 days to cover. This current reading, along with the past three, is among the lowest short interest readings for the year. Shares closed Monday at $183.36, in a 52-week trading range of $126.76 to $203.30.

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