What goes up must come down. The law of gravity applies to physics -- and the stock market.

This has been readily apparent in 2014 with biotech stocks. After taking the world by storm over the previous two years, many stocks in the sector instead now have storm clouds overhead. Several of the biggest biotechs rank among the biggest losers. Here's the countdown of the S&P 500's worst-performing biotech stocks so far in 2014.

3. Gilead Sciences (NASDAQ:GILD)

Source: Gilead Sciences. 

Gilead's hepatitis C drug Sovaldi emerged as a major success story. Unfortunately for the company's shareholders, that success attracted attention that hurt the stock. Gilead's shares have dropped 11% year to date.

Payers began to threaten to push back a few months ago over the $84,000 price tag for a 12-week-treatment with Sovaldi. For example, Express Scripts' Chief Medical Officer Steven Miller told Bloomberg that the giant pharmacy benefits manager would try to pit new hep C drugs against one another to clamp down on the high costs. 

Some members of Congress jumped on the bandwagon in March. Democratic representatives on the House Energy and Commerce Committee sent a letter to Gilead's management requesting information about the company's pricing methodology for Sovaldi. The congressional interest sent shares on a downward trajectory that the biotech still hasn't completely broken.

Source: Vertex Pharmaceuticals. 

2. Vertex Pharmaceuticals (NASDAQ:VRTX)
Count Vertex among several biotechs that got caught up in the worries about congressional action on expensive drugs. The stock was hit even harder than Gilead's, though. Vertex shares are now down 15% so far in 2014.

Vertex's greater vulnerability stems from its reliance on only two drugs -- Kalydeco and Incivek. The latter is a hepatitis C treatment that got off to a good start but has seen sales decline with the advent of newer drugs (like Sovaldi). Cystic fibrosis drug Kalydeco, on the other hand, is still gaining steam, with over $371 million in net product sales last year.

Uncertainty about upcoming clinical results could also be a factor weighing on Vertex's shares. The company expects to soon announce findings from a couple of studies featuring a combination of Kalydeco with VX-809 in treating cystic fibrosis. 

Source: Celgene. 

1. Celgene (NASDAQ:CELG)
The status of biggest biotech loser in the S&P 500, though, belongs to Celgene. Shares have dropped nearly 20% year to date.

Some of its decline no doubt stems from the overall biotech pullback. Shares also probably fell partially because the company is growing at a slower rate than in the past. Missing analyst earnings estimates by a few cents in January hurt the biotech as well.

Even good news didn't help Celgene very much. The company won U.S. approval in March for Otezla in treating psoriatic arthritis. Unfortunately, the timing of that announcement just happened to coincide with the news about the congressional request for Sovaldi pricing, which had a chilling effect on many biotech stocks.

A matter of time
Celgene, Vertex, and Gilead stand out as big losers so far in 2014. However, we should remember that's only a four-and-a-half-month period.

If we look at longer time frames, each of these stocks has been a huge winner. How have these stocks performed over the last two years? Celgene's up 76%. Vertex jumped 72%. Gilead nearly tripled. The corrections of these stocks this year are still relatively small by comparison.

Investors should also look toward the future for all three companies. Celgene's Revlimid shows no signs of slowing down. The company also claims several strong up-and-coming drugs with Abraxane, Pomalyst, and now Otezla. Good news from the Kalydeco/VX-809 clinical studies could power Vertex to huge gains. Gilead will still make billions from Sovaldi. 

All three of these stocks could ultimately experience nice rebounds -- especially Celgene and Gilead. These short-term losers are long-term winners, in my view. It's just a matter of time.