I have never done heroin but I have been around users for the past 25 years. Yes addicts can function for sure however if you are someone who has been around dope users a lot, you can spot one from a mile away. I don't mean some destitute junkie on the street, I mean a person who keeps a job and gets by and thinks no one knows he's an addict. Most people don't know but I can always spot them. First, their pupils are always ridiculously small and their skin becomes somewhat translucent. These are things that you can't really stop from happening. Many will sweat more than a normal person and some will have the tendency to itch themselves. Some also feel the need to try and cover up seeming high by talking too much and over explaining everything they do. It's hard to describe properly but unfortunately I've been around way too many people on dope. Since the early 90s I've known close to 30 people who have ODd. It's a shame. I always try and be as positive as possible and support them when they get help and the unfortunate reality is that I know only a few who have ever managed to stop using permanently. It is the worst of the worst when it comes to drugs. I would never ever take any opiate under any circumstances. I am terrified of them and have seen people who literally knew nothing about drugs become full blown dopeheads because they were prescribed opiates from a surgery, etc. When you watch your friends become drug addicts it helps you realize that drug use isn't really a criminal problem, it's a public health problem.