Is xenical or alli which are the same thing, effective for weight loss?

Depends: It's fda-approved as a weight loss medication but it works differently for different people. The prescription version works better than the over the counter Alli since it's double the strength. In general, these meds should only be used as adjunct (add on) to proper diet and exercise discretion. As of 7/22/2012, xenical is one of only 4 drugs fda-approved for weight loss.