My friend taking "height up" pills and succesful increase his height 5cm at 21 y/o. I'm also 21 y/o and goong to take those. Is it really effective?

No. People have reached their final adult heights and have already stopped growing, by the time they are 21 years old. Only in the extremely rare cases where a person has continued growing each year, from 18-20, might he grow a bit at 21. That means, if no height growth over the past year, then there will be no more growth.