Metamucil can help prevent gastrointestinal side effects of orlistat (Alli, Xenical).

  Orlistat reduces calorie intake by blocking the breakdown and absorption of dietary fats. It's a safer OTC alternative to appetite suppressants, but many people discontinue treatment due to side effects like oily stools, flatulence, and anal leakage. It's been called "Antabuse for dieters."

  Some clinicians are using psyllium (Metamucil, etc) to prevent orlistat side effects. Psyllium absorbs free fats...leading to fewer episodes of oily spotting, fecal urgency, and incontinence. Taking psyllium 6 grams with each dose of orlistat or 12 grams only at bedtime seems to reduce GI side effects by about 40 percent.

  But tell patients not to use psyllium as a means to push the envelope and eat more fats. Psyllium is likely to be less effective as fat intake increases.