Is alii effective for weight loss ?

It will help: with minor weight loss, but only as long as you take it, It can also cause some "fecal soilage".

It can help: Alli promotes weight loss by decreasing the amount of dietary fat absorbed in your intestines. Lipase, an enzyme found in the digestive tract, helps break down dietary fat into smaller components, so it can be used or stored for energy. Alli inhibits the work of lipase. When you take the drug with a meal, about 30 percent of the fat you consume isn't broken down and is eliminated through bowel

Only marginally: In reality, the data out there for orlistat(Ali is the over the counter 1/2 dose version of prescription Xenical) isn't particularly robust. It does seem to stimulate faster weight loss early on and slowed weight regain in the future but the overall effects are rather unimpressive.

Just a bit.: Alli does technically help weight loss, when used with a healthy diet and exercise regimen, but truth be told the weight loss attributable to Alli alone in studies is only a few pounds, literally. Risk of side effects may not outweigh the small weight loss benefit.