Depending on where your friend got them he might have gotten counterfit underground percocet.These will make you sick,some people violently sick for uo to a day.They look exactly the same as the real ones,but contain no real oxycodone in them,although for some reason people who take them sometimes do not get withdrawl symptoms from them if they were long term users of real percs.The only way to tell them apart is to compare side by side with real percs,they will be slightly less shiny as they have not been compressed as hard when made as real percs.the next test is to place the perc on a hard surface and press down as hard as you can on it with your thumb,if it crushes,especially to powder then it's fake.Real percs you shouldn't be able to crush,if they do break they will break into hard pieces not powder.Fwiw the market has been flooded with the fakes the last two years.