I'm a school teacher by profession. I became dependent upon Opiates (Heroin) when I was ~16 and I was dependent until ~28 and I'm 32 now. I went through college on Heroin and began my professional career without changing anything. I was also in Asia and the Middle East. I believe that many of the signs I would exhibit were construed as the eccentricities of a foreigner.
I made it to school on time, I passed my performance reviews and I had a great relationship with my students. I was definitely "functional" as I collected a paycheck and paid my bills, though that was it. My life was waking up, injecting Heroin and maybe taking some Amphetamine, going to work, injecting at lunch, coming home and injecting again, usually waking up hours later on the couch ready for more.
I had a job, a place to live and Heroin. Still, my life was completely, entirely empty. I had no friends, relationships, hobbies, interests or anything else of substance. It was just Heroin. In my opinion, I was a successful functional user. Success in this case meant a life devoid of meaning.
We ultimately use drugs to enhance our lives. If all we wanted was numbness, we would probably just skip the bullshit and kill ourselves. The hope is that using Heroin was going to make things better. At the end of it, there was nothing in my life that could be made better.
I understand this thread was a discussion regarding Methamphetamine. I will say that, if there are few "functional" Opioid addicts out there then there are even fewer for Methamphetamine. Most people I've known who began compulsively using Methamphetamine were destroyed inside and out in a relatively small amount of time. It's one of the most degrading things I've seen happen to human beings with my own eyes. They stop basic hygiene, become emaciated from malnutrition, their teeth fall out seemingly overnight, their faces become sunken in and they're left wandering around the city all night scanning the pavement for drugs.
I don't feel that "functional" use is a realistic outcome for 99.9% of people. I believe that Amphetamines can be used in a responsible manner, just like Opioids and/or Benzodiazepines. The key to making these potent drugs work is total discipline. People decide one day they want to take two instead of one and this snowballs into complete bullshit. Only when the dose is kept as low as possible and the schedule remains the same is there a chance for long-term success.
As a street drug, Methamphetamine is inherently going to vary in potency and composition. Perhaps it is straight DextroMethamphetamine and not racemic. Perhaps it is pure and perhaps not. Maybe the dealers thought throwing in some Fentanyl would be a good idea. Even if you're disciplined, you're dealing with a constantly fluctuating drug market, Basically, it's impossible to dose yourself with any kind of accuracy.
To wrap around what I said in the beginning, even if you can hold down a job and pay the rent while using Meth, your best-case scenario sees you with an empty life. If you feel you need a stimulant, then go through the process of getting one prescribed. Nothing good can come from being a daily Methamphetamine user aside from the Rock Opera I'm writing. It's about a sexy, renegade Harm Reduction consultant struggling with an advanced case of Giant Penis Syndrome. In the year 2347 Hitler reemerges in the form of an artificial super-intelligence, Keif' must journey to Jupiter to challenge both Hitler and a gigantic Mecha-Goering, ultimately beating Hitler to death with his flaccid penis.
Mecha-Goering is revealed in a twist to actually be hundreds of dwarves. The dwarves are sentenced to death by penis and the credits roll to the sound of Queen's "We Are the Champions".