Resacore, Cortaslim, et al attempt to regulate the body's production of Cortisol which is released during periods of stress. Smoke some weed. j/k
When your body produces too much Cortisol it is what is known as Cushings Syndrome.
If your bodyweight is because of too much stress, Cortisol inhibiting drugs may work. If your bodyweight is because of too much eating (two big macs a day), it won't help a bit. Obviously if your weight is due to too much Cortisol and too much food, there will be some effect.
If it is working for your friend, more power to him. Unlike other fat burners, these types of drugs don't have stimulants in them (would sort of go against the fact you are trying to reduce stress thereby reducing Cortisol).
But, do some internet searching for the cheaper varieties, I've seen resacore as high as 50/bottle and Cortaslim for as much as 40/bottle. You can find the same stuff/effects on the internet for half.
But, if it is the end all fat cure, pics above wouldn't be possible. If your friend is losing weight because of stress levels as soon as he is off, he'll gain the weight back without some type of lifestyle change.