SAN DIEGO ( TheStreet) -- The going rate the Japanese are willing to pay for development rights to a unapproved obesity drugs seems to be $50 million.

A $50 million upfront fee is what Takeda Pharmaceutical Co. will pay Orexigen Therapeutics ( OREX) to secure North American marketing rights to Contrave, Orexigen's experimental obesity drug, according to terms announced Thursday.

This partnership follows a similar deal announced in July in which Japanese drug maker Eisai also paid $50 million upfront for U.S rights to Arena Pharmaceuticals' ( ARNA) obesity drug lorcaserin.

Orexigen shares closed Wednesday at $4.59, ahead of the partnership announcement.

The relatively small upfront payments, especially for drugs already under review by the U.S. Food and Drug Administration, reflect a cautious outlook towards the approvability and commercial potential for these drugs. It's also worth noting that to date, none of the large U.S.-based pharmaceutical companies have been willing to sign obesity drug deals.

The Orexigen-Takeda partnertship leaves Vivus ( VVUS) as the only U.S.-based obesity drug developer without a larger marketing partner. An FDA advisory panel in July voted against recommending approval of Vivus' Qnexa, fearing the drug's long-term safety.

Similar FDA panels will be reviewing Arena's lorcaserin on Sept. 16 and Orexigen's Contrave on Dec. 7.

In exchange for the $50 million upfront payment, Takeda receives exclusive Contrave marketing rights to Contrave in the U.S., Canada and Mexico. Orexigen will have the right to co-promote the drug. Takeda will pay upwards of an additional $1 billion to Orexigen upon Contrave achieving certain, undisclosed, regulatory and sales-based milestones. Takeda will also pay tiered double-digit royalty payments on net sales of Contrave in North America.

Again, the future terms of the Orexigen-Takeda partnership mirror those signed earlier by Arena and Eisai.

Contrave is similar to Vivus' Qnexa in that it's a two-drug combination designed to help patients lose weight. Contrave consists of two currently approved drugs combined together to suppress appetite and fight food cravings. One of the drugs in Contrave is naltrexone, currently used to fight opioid and alcohol addiction; the other drug is the antidepressant bupropion.

Phase III studies demonstrated that Contrave helps patients lose weight, but the drug also causes an increase in blood pressure, which has raised some doubts about the drug's approvability, especially in an regulatory environment where the cardiovascular safety of weight-loss drugs is being heavily scrutinized.

On Sept. 15, an FDA panel will consider whether to allow Abbott Labs to continue selling the weight-loss drug Meridia after a long-term study tied the drug's use to an increase in heart attacks and strokes. Meridia also causes an increase in blood pressure and heart rate.

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