Darron Cummings/AP
Some customers are complaining that the new Diet Pepsi, which hit stores last week, tastes "terrible" and has a strange aftertaste.
"Diet Pepsi is awful," one customer wrote on the company's Facebook page. "I hate the new flavor."
Another wrote, "Got a bunch of the new diet Pepsi. Disgusting. Will have to return. Bring the old one back."
The revamped formula replaces the artificial sweetener aspartame with a blend of sucralose - best known by the brand name Splenda - and acesulfame potassium.
Pepsi rolled out the new formula following years of declines in soda sales. Diet Pepsi's sales fell 5.2% last year.
The company hopes that getting rid of aspartame, a widely maligned sweetener, will boost sales as Americans increasingly seek out teas and energy drinks over soda. Pepsi hasn't responded to a request for comment on this story.
"The number one thing we see from consumers is a complaint about aspartame," Pepsi North America CEO Al Carey said at an investor conference in February. "Aspartame is just one sweetener but it's the one that seems to get most of the negatives in the press and on YouTube."
But now some customers are begging Pepsi to bring back the aspartame:
So #dietpepsi tastes terrible now... Get that spike in sales @pepsi then ultra classic diet Pepsi super can be released.
- matthew cook (@matthewcooksays) August 18, 2015They've ruined @dietpepsi! The new "aspartame free" #DietPepsi has an AWFUL aftertaste. I'm switching to @DietCoke and not looking back!
- Jimmy Mack (@jcmack03) August 18, 2015Anybody else secretly thanking Diet Pepsi for removing aspartame? I can finally kick my addiction simply because it tastes so terrible.
- JLaufe (@JLaufe) August 18, 2015@pepsi the new diet Pepsi has a bad after taste... Ick
- Justin Silver (@JustinSilver915) August 17, 2015Holy sucralose, batman. The new @dietpepsi is terrible. Thanks for helping me kick my cola habit, @PepsiCo.
- Kelly L (@SmelyPiratHookr) August 18, 2015Mission complete. I found some Diet Pepsi with the old formula! Day made. Now to get rid of the case I bought with the new formula. @pepsi
- Bonnie Smith (@Vegaswench_TF) August 18, 2015I want my aspartame-laden Caffeine Free Diet @Pepsi back! The Splenda version leaves a horrible aftertaste.
- Emily Post-Haste (@mlirhar) August 17, 2015@pepsi I'm Diet Pepsi drinker & I HATE the new Diet Pepsi. There is definitely a taste difference. It tastes flat!!?? #IfItAintBrokeDontFixIt
- Teresa Gately (@tgately) August 17, 2015@pepsi avid diet Pepsi drinker, extremely disappointed with the change in flavor
- Madonna and Taylor (@Launterfied2) August 17, 2015@pepsi The new #DietPepsi is terrible. What happened? I'm addicted to the REAL Diet Pepsi. #BringAspartameBack pic.twitter.com/r1onfAq1yq
- iMarty (@Krawko) August 17, 2015