CONTACT: SHERYL WILLIAMS
         610-738-6493

FOR IMMEDIATE RELEASE

                    Cephalon Reports No Benefit from PROVIGIL
                          in Study of Adults with ADHD

            PLANS FOR LABEL EXPANSION INTO OTHER INDICATIONS ON TRACK

         West Chester, PA - July 31, 2000 - Cephalon, Inc. (NASDAQ: CEPH) today
announced that a clinical study of PROVIGIL-Registered Trademark- (modafinil)
Tablets [C-IV] in adults with attention deficit hyperactivity disorder (ADHD)
showed that compared to placebo PROVIGIL therapy showed no benefit in reducing
the symptoms of ADHD, as measured by the DSM-IV ADHD Rating Scale. The
113-patient, double-blind, placebo-controlled trial compared the safety and
efficacy of 100 mg and 400 mg doses of PROVIGIL to a placebo. PROVIGIL was
generally well-tolerated.

         Cephalon chairman and chief executive officer Frank Baldino, Jr.,
Ph.D., stated: "While we are disappointed with the results of this study, we
feel fortunate that three out of four studies with PROVIGIL reported this year -
excessive sleepiness associated with obstructive sleep apnea and shift work and
fatigue associated with multiple sclerosis - have been positive. The company is
on plan to pursue label expansion of PROVIGIL in the areas of excessive
sleepiness and fatigue. In the meantime, PROVIGIL prescriptions have been
growing steadily this year and interest among clinicians in evaluating the drug
for other indications is high."

         PROVIGIL is marketed in the United States, the United Kingdom, Austria,
Ireland and Italy for the treatment of narcolepsy or the excessive daytime
sleepiness associated with narcolepsy. The drug was approved by the Food and
Drug Administration in 1998 as a once-a-day therapy to improve wakefulness in
patients experiencing excessive daytime sleepiness associated with narcolepsy.
The most frequently reported adverse events observed in clinical trials for
narcolepsy were headache, nausea, nervousness, anxiety, infections and insomnia.

         Dr. Baldino will provide a clinical update on PROVIGIL with analysts
and investors on a conference call today beginning at 10:00 am EDT. To
participate in the call, dial 1-719-457-2622 and refer to Conference Code Number
869516.

         CEPHALON, INC., HEADQUARTERED IN WEST CHESTER, PENNSYLVANIA, IS AN
INTERNATIONAL BIOPHARMACEUTICAL COMPANY DEDICATED TO THE DISCOVERY, DEVELOPMENT
AND MARKETING OF PRODUCTS TO TREAT SLEEP DISORDERS, NEUROLOGICAL DISORDERS AND
CANCER.

                                  - CONTINUE -





Cephalon Reports No Benefit from PROVIGIL
IN STUDY OF ADULTS WITH ADHD
PAGE 2


         IN ADDITION TO HISTORICAL FACTS OR STATEMENTS OF CURRENT CONDITION,
THIS PRESS RELEASE MAY CONTAIN FORWARD-LOOKING STATEMENTS. FORWARD-LOOKING
STATEMENTS PROVIDE CEPHALON'S CURRENT EXPECTATIONS OR FORECASTS OF FUTURE
EVENTS. THESE MAY INCLUDE STATEMENTS REGARDING ANTICIPATED SCIENTIFIC PROGRESS
ON ITS RESEARCH PROGRAMS, DEVELOPMENT OF POTENTIAL PHARMACEUTICAL PRODUCTS,
INTERPRETATION OF CLINICAL RESULTS, PROSPECTS FOR REGULATORY APPROVAL,
MANUFACTURING DEVELOPMENT AND CAPABILITIES, MARKET PROSPECTS FOR ITS PRODUCTS,
SALES AND EARNINGS PROJECTIONS, AND OTHER STATEMENTS REGARDING MATTERS THAT ARE
NOT HISTORICAL FACTS. YOU MAY IDENTIFY SOME OF THESE FORWARD-LOOKING STATEMENTS
BY THE USE OF WORDS IN THE STATEMENTS SUCH AS "ANTICIPATE," "ESTIMATE,"
"EXPECT," "PROJECT," "INTEND," "PLAN," "BELIEVE" OR OTHER WORDS AND TERMS OF
SIMILAR MEANING. CEPHALON'S PERFORMANCE AND FINANCIAL RESULTS COULD DIFFER
MATERIALLY FROM THOSE REFLECTED IN THESE FORWARD-LOOKING STATEMENTS DUE TO
GENERAL FINANCIAL, ECONOMIC, REGULATORY AND POLITICAL CONDITIONS AFFECTING THE
BIOTECHNOLOGY AND PHARMACEUTICAL INDUSTRIES AS WELL AS MORE SPECIFIC RISKS AND
UNCERTAINTIES SUCH AS THOSE SET FORTH BELOW AND IN ITS REPORTS ON FORM 8-K, 10-Q
AND 10-K FILED WITH THE U.S. SECURITIES AND EXCHANGE COMMISSION. GIVEN THESE
RISKS AND UNCERTAINTIES, ANY OR ALL OF THESE FORWARD-LOOKING STATEMENTS MAY
PROVE TO BE INCORRECT. THEREFORE, YOU SHOULD NOT RELY ON ANY SUCH FACTORS OR
FORWARD-LOOKING STATEMENTS. FURTHERMORE, CEPHALON DOES NOT INTEND (AND IT IS NOT
OBLIGATED) TO UPDATE PUBLICLY ANY FORWARD-LOOKING STATEMENTS. THIS DISCUSSION IS
PERMITTED BY THE PRIVATE SECURITIES LITIGATION REFORM ACT OF 1995.

         NOTE: CEPHALON'S PRESS RELEASES ARE POSTED ON THE INTERNET AT THE
COMPANY'S WEB SITE AT WWW.CEPHALON.COM. THEY ARE ALSO AVAILABLE BY FAX 24 HOURS
A DAY AT NO CHARGE BY CALLING PR NEWSWIRE'S COMPANY NEWS ON-CALL AT
800-758-5804, EXTENSION 134563.