Arrowhead Research Corp.’s stock has been on a roller coaster that rivals any ride at Magic Mountain.

Gains the stock saw last week on news that regulators had greenlit the Pasadena pharmaceutical company’s new clinical study were wiped out April 14 after Jefferies Group’s new analyst covering the stock promptly downgraded it.

Overall, Arrowhead’s stock fell 11 percent for the week ended April 15 to close at $7.09, making it one of the top losers on the LABJ Stock Index. (See page 44.)

The new Jefferies analyst revised the stock’s target price from $30 to $9, a massive reassessment, but one that brought it in line with other investment banks. RBC Capital Markets and Piper Jaffray had set targets of $9 and $12, respectively.

Still, said Vincent Anzalone, Arrowhead’s vice president of investor relations, Jefferies’ analysis doesn’t take into account the value of the biotech firm’s drug development platform or cash on hand, which was $104 million as of Dec 31.

“They’re being conservative,” he said. “I think the market perceived that as a downgrade when in actuality it was a new analyst assuming coverage.”

Another culprit could’ve been volatility from trading as a group of options were set to expire last week.

“Trading in our options has been relatively active over the last handful of periods and that could be contributing to some volatility,” Anzalone said.

Arrowhead shares got a boost earlier in the year on speculation that the company was a takeover target for Foster City’s Gilead Sciences Inc. Shares rose as high as $9.06, only to be sent spiraling down a week later to $6.90 when the Food and Drug Administration asked Arrowhead to proceed with a test of a lower dose of its lead drug candidate in a new study.

Arrowhead is using its own drug delivery technology to develop therapies based on an RNA mechanism that silences disease-causing genes.

“I think the good thing about biotech there’s always an opportunity for redemption,” said Anzalone, whose brother Christopher is Arrowhead’s chief executive.