A/N: I apologize profusely for not being able to subscript the chemical formulas. I've tried.
When bored: C17H21NO4 (common name: cocaine)
During sensory overload: C17H19NO3 (common name: morphine)
End result: cessation of overly troublesome neurological activity
Side effects: potential addiction
He'd tried cocaine at sixteen, out of desperation. Not even the streets of a foreign city could hold the mind of Sherlock Holmes in one place for very long. His mind felt like it was ripping itself to shreds for lack of anything to do. He had no focus, no purpose, and the agony of it was that when he was in this sort of state, this sensation of psychological cannibalism. He'd found someone almost by accident as he was roaming the streets of Berlin in a frenzy, on the verge of robbing a bank just because he was bored. But then, the dealer had seen him, approached him, made the suggestion. He was so desperate that he took it, handed over the money, and took a quick lesson in how to get high fast.
He loved it.
His brain was no longer tied in an aching knot like a muscle cramping from inactivity. He was disconnected, floating, running along neurons, leaping the synapses, free from the turmoil of understimulation. It was heaven.
He'd tried morphine at nineteen. It was his first sensory attack away from home, the first time that his mind had fully assaulted him that he couldn't hide inside his mother's antianxiety pills and the sanctity of his bedroom. He couldn't move. It hurt. He couldn't breathe properly. It hurt. The sounds of student living were painfully loud, and the smells just as bad. He was in total agony, and the only cause was his mind. Victor Trevor, his friend, saw him in the bed, having come to check on him, and didn't understand what was happening. So he ran for the nurse who also didn't understand. She merely saw that he was in pain and administered morphine.
He loved it.
Where once was painful clarity, the awareness of every single sensation, now was muffled bliss. He could no longer feel every fiber of his blankets, every little shift in temperature between inhaling and exhaling. It was heaven.
After he left university, the pain of boredom was absolute torment. No job. No friends to speak of. Telly was boring. Books were boring. Even the violin was boring. And then he remembered that night in Berlin and how free he felt with the cocaine in his bloodstream.
He sought the fine white powder and a needle with which to administer it as quickly as possible. He needed out of his Hell and he needed it now. Returning to his run-down flat, he ran back into his memory of that night, trying to find the mental instruction manual on the correct procedure, and eventually finding it and acting on it.
It became his new favourite pastime.
Again, his mind attacked him. Again the pain of existing was too much to bear. The attacks grew farther apart as he grew older, but they also grew far worse. Twenty-two and in so much pain he thought he would rather die than live another moment. He was just too pained to do anything about it. Then he remembered that day in university and the muffling effect of the morphine.
He gathered the strength to get out of bed to find a way to get it. He was in pain, that much was obvious to anyone. The hospital seemed easiest, and even if there was nothing visibly wrong with him, they would at least give him something for a while.
He had a better night's sleep that night than he had in years.
The need to stimulate his mind became addictive. It always had been, but he'd never had an easy (if expensive) out before. Almost every afternoon, he'd shoot up, welcoming the pleasant tingle of his mind as the ceiling danced into sparkling clarity, the universe dancing with possibilities far above those of the average human mind.
But the high had a consequence. He had very little money for anything else besides the necessities and the drugs. He'd grow agitated within a day. He found himself shouting at Mycroft for no good reason, shouting at his mother, when she called, shouting at strangers on the street for looking at him.
He was addicted.
The attacks grew more frequent as his body adjusted to the cocaine highs. Now it seemed that once a week, he'd leave the house to get some hospital to admit him just so he could get the morphine. It didn't occur to him to have a private stash. He just needed his mind to stop fighting him.
Hospitals were beginning to turn him away now for drug-seeking behavior. They didn't understand the agony. They didn't understand the desperation. He had to keep himself from fighting them to let him in. That one dreamy moment was starting to get further and further away.
He was addicted.
He awoke in hospital one day, unable at first to remember why he was there. It wasn't for the morphine—his head hurt. His chest hurt. He was tired and achy and felt as though he'd been dipped in acid. He tried to move, but it was difficult. He felt burnt-out, lifeless. And then he softly cursed himself as he realized what had happened.
Overdose.
He'd broken his leg. On purpose. It hurt like hell, especially today, but he needed the hospital to admit him, to give him the morphine he so desperately craved. He'd done more damage than intended, the calculations off, and as he lumbered into the emergency room, the pain of everything shot through him like a bullet and his brain could no longer stand it.
He passed out.
He was clean now, of course, and living with a doctor who could tell the instant he wasn't. He'd be lying if he said he was never tempted to go back to cocaine, the endless mind-numbing tedium of reality once again caustic to his mind, but he'd learned that if he was going to indulge that addiction to wait until John had left the country for one reason or another.
When John was in New Zealand, he buckled to the boredom. No one but Mrs. Hudson even suspected. And she didn't know the truth of it. Not until she found the needle in the rubbish and confronted him. Or tried. He evaded.
Someone knew.
His body screamed again, the first time since moving into 221B. He could hear the drip in the kitchen sink, and it was deafening. He could feel the weave in his sheets. He could smell Speedy's next door. The cold air going down his trachea was like knives. John knocked on the door, resulting in a half-whimper—this was the worst overload he'd ever experienced.
"You okay?"
"Morphine."
"What?"
"Not so loud. Morphine. Please."
John didn't know about the addiction. John just saw his friend in pain, and saw that Sherlock knew the best way to ease that pain. So he administered the drug after a long debate with himself.
Sherlock smiled as he felt his senses numbing.
He had a way out.