Why is heroin still used in medicine

I don’t understand why heroin is still used in medicine when so many other drugs similar to it also exist. Heroin is illegal almost everywhere in the world, some countries allow it for ceremonial use or medical use in some cases though. I understand some of these other drugs may have side effects, but morphine has barely any side effects and from what I understand is also better than heroin in many ways. <br><br>I remember seeing a documentary on underground heroin manufacturers and they were saying how they use what I think was opium and mix it together and use acetic acid to make heroin, the documentary also showed a picture of a bottle of what they were using and it was prescription morphine.