Exhibit 10.3

AMENDMENT NO. 3

TO THE TOLL MANUFACTURING AGREEMENT

This Amendment No. 3 (the “Amendment”), effective as of January 1, 2011, is by
and between Arena Pharmaceuticals GmbH (“ARENA”) and Siegfried Ltd.
(“SIEGFRIED”), and modifies the Toll Manufacturing Agreement, dated January 7,
2008, as amended, by and between ARENA and SIEGFRIED (the “Agreement”). All
capitalized terms used herein and not otherwise defined shall have the meanings
set forth in the Agreement.

WHEREAS, subject to the Parties’ concurrent execution of Amendment No. 2 to the
Technical Services Agreement between ARENA and SIEGFRIED, dated January 7, 2008,
as amended, and Amendment No. 1 to the Asset Purchase Agreement between ARENA
and SIEGFRIED, dated December 18, 2007, the Parties wish to amend the Agreement.

NOW, THEREFORE, in consideration of the promises and the mutual covenants set
forth herein, the receipt and sufficiency of which are hereby acknowledged, the
Parties agree as follows:

1. The last sentence of Article 2.1 paragraph 1 is replaced with the following
sentence:

“During the period commencing on January 1, 2012 and ending June 30, 2012,
SIEGFRIED shall use its reasonable commercial effort to order from ARENA
200 million units of Products.”

2. In paragraph 2 of Article 2.1, the language “2011 and thereafter: no cost
guarantee” is replaced with the following language:

“In 2011 and thereafter: no cost guarantee, but SIEGFRIED guarantees to order
Products for production by ARENA in 2011, in the amount of 400 million units,
which amounts Arena will, irrespective of anything to the contrary in the
Agreement (including the last sentence of the first paragraph of Section 3.1),
manufacture and supply as ordered by Siegfried, provided always Siegfried
complies with provisions of Lead Delivery Time Periods and reasonably
distributes orders over 2011. For purposes of determining whether the guaranteed
units have been ordered, Tamsulosine will not be included. Subject to the
maximum quantities, Lead Delivery Time Period and other limitations on Products
provided in this Agreement, ARENA agrees to use commercially reasonable efforts
to supply up to 150% of such guaranteed units in 2011 if so requested by
SIEGFRIED and up to 150% of the 200 million units of Products in the first half
of 2012.”

3. Article 2.6 is replaced with the following language:

“2.6 “Term.

(a) This Agreement is entered into for indefinite period of time.

--------------------------------------------------------------------------------

(b) As from December 31, 2010, either Party may terminate this Agreement upon
giving six (6) months prior notice at any time, in a Party’s discretion and for
any reason or for no reason, with an effective termination date no earlier than
June 30, 2012. In addition, upon giving the number of months notice as specified
in Appendix A, ARENA shall be entitled to terminate its obligations with regard
to certain Products effective on or after June 30, 2012; with regard to
Gabitril, however, effective on or after August 11, 2012 only, and with regard
to Idebenon effective on or after December 31, 2012 only (provided the foregoing
obligation is subject to the last sentence of the first paragraph of
Section 3.1).

(c) In the event ARENA’s obligations are terminated with regard to certain
Product(s) and not with regard to the entire Agreement, the maximum quantities
of remaining Products that SIEGFRIED may order shall be reduced based on the
most recent 12 months forecast issued before the termination is communicated to
SIEGFRIED.

(d) SIEGFRIED’s continued performance under the Technical Services Agreement
between ARENA and SIEGFRIED dated January 7, 2008, as amended (the “TSA”), if so
requested by ARENA, is a condition precedent to ARENA’s continued performance
under this Agreement after December 31, 2010.

(e) If ARENA is asked to manufacture validation lots of Product(s) under this
Agreement, the standard cost and any additional costs for relevant Services of
ARENA for such lots must be agreed in advance between the parties.”

4. In Article 5.2, the language “In 2011: no minimum capacity anymore after
2010” is deleted.

5. Article 6.2 is restated in its entirety as follows:

“6.2 Sales Price.

(i) The Products shall be sold to SIEGFRIED at the Sales Prices. Such Sales
Prices are net of VAT. An amount equal to the VAT shall be added to the invoice
and paid by SIEGFRIED.

(ii) The Sales Prices charged to SIEGFRIED in 2011 shall be prices charged, on a
stock keeping unit (hereinafter “SKU”) by SKU basis, for each Product in 2010.
The Sales Prices for 2011 for each SKU shall be agreed upon by the parties and
attached hereto as Appendix 1 promptly following execution of this Amendment.
The Parties are aware that the prices in subsequent years may decrease as a
result of e.g. improved cost structures, or increase as a result of increased
direct costs. Not later than November 30, 2011 (and November 30 of subsequent
years, if applicable), SIEGFRIED will propose Sales Prices, on a SKU by SKU
basis, for consideration by ARENA. The Parties shall discuss and agree upon
pricing for the following year not later than December 31, 2011 (and December 31
of subsequent years, if applicable). Sales Prices for Product manufactured after
2011 shall be agreed in writing by amendment to this Agreement.

--------------------------------------------------------------------------------

(iii) With respect to this Section 6.2(iii), the term “Main Products” shall
refer to Felodipine, Fluoxetine, Doxazosine and Nifedipine. Notwithstanding
anything to the contrary herein, for Main Products manufactured during the
period beginning January 1, 2011 and ending on June 30, 2012, the prices charged
by ARENA shall be equal to the Sales Price for the product (as set forth on
Appendix 1), reduced by (1) 20% for bulk products and (2) 40% for packaged
products (price without bulk part, whereby bulk part carries discount of 20%).
The Parties may mutually agree to extend such discounted pricing after 2011,
and/or that additional Products be included as Main Products hereunder; any such
agreement must be in writing by amendment to this Agreement.

(iv) The Parties agree that it may be in the best interests of both Parties if
additional volume of Products are manufactured and sold under this Agreement,
even if the price for such Products is reduced. ARENA and SIEGFRIED agree to
consider additional price reductions which may result in greater volume of
Products being manufactured under this Agreement. The parties may agree to share
equally in the effects of such reductions; any such agreement must be in writing
by amendment to this Agreement. For example, consider a Product that SIEGFRIED
would sell to its customer for 120 CHF, and which has a Sales Price of 80 CHF.
If SIEGFRIED’s ability to secure an order for significant volumes of that
Product is contingent upon SIEGFRIED being able to sell that particular Product
to its customer for 100 CHF, ARENA and SIEGFRIED may agree that the Product’s
Sales Price is 70 CHF and for Siegfried to sell the Product to its customer for
100 CHF.”

6. Article 5.3 is restated in its entirety as follows:

“5.3 Forecast. As from January 1, 2011, on a quarterly basis SIEGFRIED shall
provide ARENA with Product forecasts covering the following eighteen months. The
forecasts shall be binding regarding the first six months, not changed during
such first six months in time and in quantity by more than +/- 20%, and with
respect to the first three months of the forecasts, the forecasts shall be a
binding order for the Products as forecasted. With respect to the last twelve
months of each forecast, the forecasted amount is a non-binding declaration of
an intention to order the forecasted amounts.

If at any time SIEGFRIED finds that a forecast is inaccurate, it shall inform
ARENA without delay and submit a modified forecast for the period in question.”

7. Appendix G is deleted from the Agreement.

8. Unless otherwise specifically amended herein, all of the terms and conditions
of the Agreement shall remain in full force and effect.

9. This Amendment becomes effective, if Amendment No. 1 to the Asset Purchase
Agreement and Amendment No. 2 to the Technical Services Agreement have already
been or are entered into within three business days after execution of this
Amendment the latest.

--------------------------------------------------------------------------------

10. This Amendment may be executed in multiple counterparts, each of which shall
be considered and shall have the same force and effect of an original.

11. This Amendment shall be governed by the laws of Switzerland under the
exclusion of the UN Convention on Agreements for the International Sale of Goods
(the so-called Vienna Convention).

IN WITNESS WHEREOF, the undersigned, intending to be legally bound, have
executed, or caused to be duly executed, this Amendment.

 

Siegfried Ltd.   Arena Pharmaceuticals GmbH By:   /s/ Hubert Stückler   By:  
/s/ Daniel Müller Name:   Hubert Stückler   Name:   Daniel Müller Date:   March
11, 2011   Date:   March 11, 2011 By:   /s/ Hans-Rudolf Kern   By:   /s/ Arnaud
Schattmeier Name:   Hans-Rudolf Kern   Name:   Arnaud Schattmeier Date:   March
11, 2011   Date:   March 11, 2011

--------------------------------------------------------------------------------

Appendix 1

Sales Prices for 2011