Finally he thrust the sharp point home, pressed down the tiny piston, and sank back into the velvet-lined arm-chair with a long sigh of satisfaction. [...]

"Which is it to-day?" I asked,-"morphine or cocaine?"

He raised his eyes languidly from the old black-letter volume which he had opened. "It is cocaine," he said,-"a seven-per-cent solution. Would you care to try it?"

-The Sign of the Four

"Got something for you." Passing by, John dropped a small paper bag on the table.

Sherlock eyed it suspiciously. "What's that, then?"

"Try that instead of those dreadful nicotine patches," John yelled from the kitchen where he was unpacking the rest of his shopping.

Sherlock spilled the contents of the bag onto the table. He picked up one of the small brown beans and sniffed them. "Are these cocoa beans?"

"They're good for you!" came the answer from the kitchen.

"Cocoa beans? Seriously?" Sherlock came after John and shoved one of the beans into John's face. "You want me to replace nicotine with theobromine? That has the effect of what, a really weak cup of coffee? Plus," he said, handing John the bean, "they taste like earwax."

"Oh, and smoking tastes like milk and honey?" John held out the bean to Sherlock. "Theobromine reduces the risk of cancer, it's good for your heart and also good for the brain. Nicotine is pure poison. Have more beans if they're too weak for you."

"That's your advice to me, drug-wise? Just take more? Have you never heard of chocolate poisoning?" Sherlock returned to the couch and popped a bean in his mouth.

"Really, Mr. Three-patches-at-once?" John stuck his head in from the kitchen, "You're worried you might overdose on cocoa beans?"

He joined Sherlock in the living-room with a glass of wine and sat down on a chair. "With your age and stature, I'd say you'd have to eat at least 10kg of cocoa beans to be in any danger of poisoning."

"And how many do I have to eat for a three-patch problem? Because I think it's a lot more"

John sighed. "Fine. Stick to your ways. Never mind me. I just thought that your substance abuse habit could do with a bit of change."

"Says the man who's been drinking the same Beaune vintage for weeks. Besides, what do you know about my substance abuse habit?"

"I don't know much," John admitted. "I know that you used to take drugs and I know that you claim to be clean now. But," he added with a wry smile, "I could try some deductive reasoning, now, couldn't I?"

Sherlock raised an eyebrow. "I'm intrigued, doctor. Deduct away."

"Well," John began.

"Hold on." Sherlock handed John a cocoa bean. "Here, take this. You might need it to help you think. Unless you'd prefer a breath of fresh air, which might be slightly more stimulating."

John gave him an exasperated look but took the bean anyway and started chewing on it.

"Well," he began again, "Let's have a look at what type of drugs you prefer. I can rule out hallucinogens. You rely heavily on your senses for your work, changes in perception and consciousness would render you practically useless.

"I can see you using depressants to take the edge of the boredom you're feeling when you're not working on a problem."

"Can you," Sherlock said, without giving anything away.

"Alcohol and barbiturates consumed in large enough quantities to cause sedation also tend cause confusion, nausea and worst of all anterograde amnesia. You like to be in control, not knowing what you did or what happened would be a problem.

"Same goes for benzodiazepines, only in long term use they also cause cognitive impairments, and we can't have that, can we?"

"You know," Sherlock interrupted, "you're really taking all the fun out of it by using those horrible medical terms. They're so very unpoetic."

"I am deductive reasoning here," John said, "so let's not talk about 'devil's spunk' or whatever and stay scientific, ok?"

"Right." Sherlock nodded sarcastically. "Scientific."

"Now," John started ticking off his fingers, "alcohol, barbiturates, benzodiazepines. That really only leaves us with opioids.

"There's the mild to medium opioids, like codeine, hydrocodone and oxycodone. They're pretty easily available but they're usually mixed with paracetamol, you'd have to be really careful with the dosage so you don't kill your liver.

"Besides, you're not really the type to go for the cough syrup anyway. No, you want the good stuff: Heroin or Morphine. Heroin is really just morphine in disguise, but metabolizing diacetylmorphine causes a strong sense euphoria, which is why many users prefer it. There's only one big problem with heroin: it's virtually impossible to get it pure. It's almost always contaminated with by-products or diluted with cutting agents. And I don't believe you would inject yourself with something if you don't really know what's in it. I'm putting my money on morphine."

Sherlock gave him one of his looks. "No, no, no John! Don't be so stupid!" he said in a berating tone, "Look at what's right in front of you. Think!"

For a long moment, John stared back at him. Then he smiled uncertainly. "Unless," he began, "unless you happen to be an experienced chemist with a laboratory for a kitchen and know exactly what it is you're injecting yourself with because you made it."

"There you go," Sherlock said. "Good boy. Have a bean."

"Really," John said, chewing. "You made your own heroin. In your kitchen."

"Of course I did. But I don't think you're finished yet, doctor." He gave John an encouraging look. "Do go on. But don't use terms like 'metabolizing diacetylmorphine' for one of the most beautiful things in the world again. Really don't."

John sighed. "Fine," he said, "Let's put aside the homebrew heroin and look at what you're currently using: large amounts of nicotine, some caffeine. So you might enjoy the occasional downer but I'd say that you're mostly a stimulants man.

"I don't see you using ecstasy. It's an emphatic drug and somehow I can't picture you enjoying connecting better with other people.

"Then there's methylphenidate. Stealing Ritalin from some kid seems up your alley, but that stuff has a list of side-effects the size of my arm." He ticked off his fingers. "Abdominal pain, anxiety, cardiac arrhythmia, dizziness, tachycardia and so on. That leaves amphetamines and cocaine.

"Amphetamines cause longer highs, but they're a very physical drug, stimulate the body rather than the mind. Maybe to work through the nights when you're on a case, although I've seen you do that on adrenaline alone. So, cocaine.

"Problem with cocaine is, users build up tolerance quickly," John continued, chewing. "You have to start taking more pretty soon."

He paused for a moment and gave Sherlock a thoughtful look. An amused smile was playing on Sherlock's lips. "There's a much more elegant way."

"I suppose," John said after giving it some thought, "you can achieve more intense highs by finding ways to ingest it faster. Injection and inhalation are both faster than mucosal ingestion. It's usually said that the fastest way to the brain is through the lung, but I wouldn't put it past you to try and put a needle in your own carotid artery.

"Only, that merely defers the problem. Since we already established an H-lab in your kitchen, I suppose you could do some tricks with the right solving agent, but at some point you are inevitably back to upping the dosage.

"And the faster you ingest it, the shorter the effect. Intravenously, using the right solution, I'm guessing a couple of minutes, tops."

Sherlock nodded. "Hangovers get worse, too." He smiled mischievously. "There's always something."

"So you decided to clean up."

"Only logical conclusion."

"And detoxing from two of the most addictive substances out there, I don't suppose you sought out professional help? In an addiction treatment centre, perhaps?"

Sherlock frowned at him. "Of course not. You just stop using. Having your hand held doesn't make any difference."

"Right," John said, "addicts of the world, rejoice. You can just stop using." He shook his head. "Consider me quite impressed, though."

"Now that you're done with the hard detecting work," Sherlock said, "I don't think we need this anymore," He closed up the bag of cocoa beans. "Instead," he said, taking John's glass off him and emptying it in one go, "why don't you get us some more wine?"