What is a "normal" human being? There are plenty of people who don't use drugs who are not functioning well or happy. I think a "functional addict" is just someone whose life has not been ruined by their addiction and they appear (to outsiders at least) to have a relatively normal life. Their drug use does not appear to be having a huge impact on other people. It can be someone who is physically or mentally dependent on a substance but doesn't have the extreme adverse impacts on their life stereotypically associated with addiction. "Functional addict" is kind of a problematic term, but to me it just means someone is still able to have a home, a job, a relationship, etc. Maybe they are self-medicating and their life is not all that different from the life of someone who is legitimately prescribed a similar drug. "Functional addict" can also be used to mean someone who uses drugs solely to feel normal and does not appear high or inebriated. The term is not ideal, but it is useful in reminding people than not everyone with an addiction is the same or fits the stereotype (in fact most don't fit the stereotype) and that there are many drug addicts/users out there who do not appear as obvious drug addicts. Being "functional" does not mean you are not addicted or that there is no reason to quit, however. There may be subtle adverse consequences to the person's drug use, such as feeling dependent on/controlled by something, needing a supply of the drug to function normally, spending more money than you would like on drugs, being limited as far as travel or anything else that would impact one's access to the drug, etc. While the "functional addict" is not completely out of control, they are still dependent on their drug, and that dependence is more likely to show itself when the person is under stress or does not have access to the drug. Their behaviour surrounding drugs is still not completely rational, as it is rare, if not impossible, for an addiction or dependence to an illicit drug to have no adverse consequences at all and they may no longer even be getting any benefits from the drug other than preventing withdrawal. And being a "functional addict" certainly doesn't mean it will always stay that way.
I was, for a long period of my heroin addiction, what some would consider a "functional addict". Others did not suspect me of being a drug addict, I still looked healthy, I didn't appear "high" around others and I was still able to have a good job, a home, and normal relationships. But it still impacted my life adversely, even if it wasn't obvious to other people. I wasn't free.
One thing about using a drug recreationally is that it can be very hard to sustain once you have been addicted in the past. It is extremely difficult to go back to using just for fun or occasionally for any period of time. You (the OP) need to decide and be honest with yourself about whether or not your drug use is problematic and whether or not it is worth the risk of becoming addicted.
