Hi GWTWND,
Alli will still be blocking 25% of the fat, but with time and weight loss your body adapts. In order to continue losing weight you need to consuming less calories and exercising more (increased intensity).
Have you gone to a lower caloric level? To get over this plateau you may need to decrease your caloric intake by 200 calories a day. Have you been exercising at least 30 minutes a day (aerobic) and resistance training (2-3 times a week)?A little tweaking will get you back on track.
Hope this helps.
Sophia De Monte RPh