Filed by Sanofi-Synthelabo Pursuant to Rule 165 and Rule 425(a) under the United States Securities Act of 1933, as amended Subject Company: Aventis Commission File No. 001-10378 Date: June 14, 2004 On June 14, 2004, Sanofi-Synthelabo issued the following press release. In connection with the proposed acquisition of Aventis, Sanofi-Synthelabo has filed with the United States Securities and Exchange Commission (SEC), a registration statement on Form F-4 (File no: 333-112314), which includes a prospectus and a prospectus supplement relating to the revised offer, and related exchange offer materials, to register the Sanofi-Synthelabo ordinary shares (including Sanofi-Synthelabo ordinary shares represented by Sanofi-Synthelabo ADSs) to be issued in exchange for Aventis ordinary shares held by holders located in the United States and for Aventis ADSs held by holders wherever located and has also filed with the SEC a Statement on Schedule TO. INVESTORS AND HOLDERS OF AVENTIS SECURITIES ARE STRONGLY ADVISED TO READ THE REGISTRATION STATEMENT AND THE PROSPECTUS AND PROSPECTUS SUPPLEMENT RELATING TO THE REVISED OFFER, THE STATEMENT ON SCHEDULE TO, AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, AS WELL AS ANY AMENDMENTS AND SUPPLEMENTS BECAUSE THEY CONTAIN IMPORTANT INFORMATION. Investors and holders of Aventis securities may obtain free copies of the registration statement, the prospectus, the prospectus supplement relating to the revised offer and related exchange offer materials, and the Statement on Schedule TO, as well as other relevant documents filed with the SEC, at the SEC's web site at www.sec.gov. The prospectus, the prospectus supplement relating to the revised offer and other transaction-related documents are being mailed to Aventis securityholders eligible to participate in the U.S. offer and additional copies may be obtained for free from MacKenzie Partners, Inc., the information agent for the U.S. offer, at the following address: 105, Madison Avenue, New York, New York 10016; telephone 1-(212) 929-5500 (call collect) or 1-(800) 322-2885 (toll-free call); e-mail proxy@mackenziepartners.com. * * * * [SANOFI-SYNTHELABO LOGO] [graphic] Investor Relations SANOFI-SYNTHELABO'S OFFER FOR AVENTIS ADJUSTMENT OF OFFER TERMS ON APPROVAL OF AVENTIS DIVIDEND PARIS, FRANCE-- JUNE 14, 2004-- Sanofi-Synthelabo (PARIS: SAN, NYSE: SNY) announces that at the Aventis (PARIS: AVE, FRANKFURT: AVE.ETR, NYSE: AVE) annual general meeting held on June 11, 2004, the shareholders of Aventis voted to approve Aventis's 2003 dividend in the amount of (euro)0.82 per share, with an ex-dividend date of June 15, 2004 and a payment date of July 15, 2004. As a result, in accordance with the terms of Sanofi-Synthelabo's revised offer for Aventis, the terms of Sanofi-Synthelabo's offer for Aventis have been adjusted in the following manner: o Standard entitlement: 5 Sanofi-Synthelabo ordinary shares and (euro)115.08 in cash for 6 Aventis ordinary shares (or 0.8333 of a Sanofi-Synthelabo ordinary share and (euro)19.18 in cash for each Aventis ordinary share; and 1.6667 Sanofi-Synthelabo ADSs and an amount in U.S. dollars equal to (euro)19.18 in cash for each Aventis ADS) o All stock election: 1.1600 Sanofi-Synthelabo ordinary shares for each Aventis ordinary share (or 2.3200 Sanofi-Synthelabo ADSs for each Aventis ADS) o All cash election: (euro)68.11 in cash for each Aventis ordinary share (or an amount in U.S. dollars equal to (euro)68.11 in cash for each Aventis ADS). This adjustment is more fully described in Section 1.3.2(a) "Terms of the New Offer for Aventis Shares" in the French prospectus supplement that obtained the AMF's visa (no. 04-384) on May 7, 2004 and under the section entitled "The Revised U.S. Offer -- Consideration Offered after Approval of Aventis Dividends" in the U.S. prospectus supplement dated May 27, 2004. In accordance with article 7 of the COB rule no. 2002-04, this press release was transmitted to the Autorite des marches financiers (AMF) before its publication. IMPORTANT INFORMATION: In connection with the proposed acquisition of Aventis, Sanofi-Synthelabo has filed a registration statement on Form F-4 (File no. 333-112314), including a prospectus and a prospectus supplement relating to the revised offer, and will file additional documents with the SEC. INVESTORS ARE URGED TO READ THE REGISTRATION STATEMENT, INCLUDING THE PROSPECTUS AND THE PROSPECTUS SUPPLEMENT RELATING TO THE REVISED OFFER, AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING ALL AMENDMENTS AND SUPPLEMENTS, BECAUSE THEY CONTAIN IMPORTANT INFORMATION. Free copies of the registration statement, as well as other relevant documents filed with the SEC, may be obtained at the SEC's web site at www.sec.gov. The prospectus and the prospectus supplement relating to the revised offer and other transaction-related documents are being mailed to Aventis security holders eligible to participate in the U.S. offer and additional copies may be obtained for free from MacKenzie Partners, Inc., the information agent for the U.S. offer, at the following address: 105, Madison Avenue, New York, New York 10016; telephone: 1-(212) 929-5500 (call collect) or 1-(800) 322-2885 (toll-free call); e-mail proxy@mackenziepartners.com. In France, holders of Aventis securities are requested, with respect to the offer, to refer to the prospectus supplement (note d'information complementaire), which has been granted visa number 04-384 by the Autorite des marches financiers ("AMF") and which is available on the website of the AMF (www.amf-france.org) and without cost from: BNP Paribas Securities Services, GIS-Emetteurs, Service Logistique, Les Collines de l'Arche, 75450 Paris Cedex 9 and to the recommendation statement (note d'information en reponse) which has been granted visa number 04-510. The public offer to holders of Aventis ordinary shares located in Germany (the "German Offer") is being made in accordance with applicable German law and pursuant to an offer document/sales prospectus, which is available free of charge at BNP Paribas Securities Services, Gruneburgweg 14, D-60322 Frankfurt am Main (Fax: 069 - 152 05 277) and on the website of the Company (www.sanofi-synthelabo.com). Any decision to tender Aventis ordinary shares in exchange for Sanofi-Synthelabo ordinary shares under the German Offer must be taken exclusively with regard to the terms and conditions of the German Offer, as well as with regard to the information included in the offer document/sales prospectus, including any amendments thereto, issued in Germany. The French Offer, the U.S. Offer and the German Offer are being made on substantially the same terms and completion of these offers is subject to the same conditions. It is intended that the three offers will expire at the same time. Investors and security holders may obtain a free copy of the Form 20-F filed with the SEC on April 2, 2004 and any other documents filed by Sanofi-Synthelabo with the SEC at www.sec.gov as well as of the Reference Document filed with the AMF on April 2, 2004 (No. 04-0391) at www.amf-france.org or directly from Sanofi-Synthelabo on our web site at: www.sanofi-synthelabo.com. INVESTOR RELATIONS DEPARTMENT Philippe Goupit Director of Investor Relations Arnaud Delepine Investor Relations Europe Sanjay Gupta Investor Relations US Anne d'Halluin-Sulzer Investor Relations CONTACTS: Email: investor-relations@sanofi-synthelabo.com Europe US Tel: + 33 1 53 77 45 45 Tel: + 1 212 551 40 18 Fax: + 33 1 53 77 42 96 Fax: + 1 646 487 40 18