I trained and am based in the UK and so my knowledge only really extends to the drugs which are available here. The basic principles, however, are applicable world-wide.
Mild to Moderate pain
The mainstay of everyday treatment of headaches, hangovers, sprains and strains is paracetamol or ibuprofen.
Both of these drugs work by interfering with prostaglandin production, which is a group of chemicals released in the body in response to trauma, producing inflammation, fever and pain.
Paracetamol is more specific in that it works primarily in the brain, to reduce fever and our perception of pain.
When taken in the correct doses – no more than 1 gram per dose for an adult and no more than 4 doses in a 24-hour period – it is a very safe drug with few side effects.
Paracetamol is removed from the body by the liver and the mechanism is overwhelmed when too much drug is present. Overdose is the most common cause of severe, acute liver failure in the western world. Unless treated very promptly and aggressively, poisoning may result in death from liver failure.
Ibuprofen is a member of the group of drugs called non-steroidal anti-inflammatories (NSAIDs) and blocks prostaglandin production throughout the body. As well as reducing our perception of pain, it actively reduces the inflammation produced in response to injury and reduces fever.
Unless prescribed by a doctor, the maximum dose for an adult is 400mg up to three times a day. At this dose, for a short period of time, it is well tolerated by most people.
Unfortunately, one of the chemicals which is blocked by this group of drugs is the one that the stomach produces to protect itself against the acid it produces in the first stage of digesting our food.
At higher doses, or if stronger NSAIDs are used, the incidence of indigestion and even ulcers and bleeding is much higher. When these drugs are used regularly for longer periods of time, a doctor will also prescribe something to protect the stomach, such as omeprazole.
Because Sherlock eats irregularly, I think that John would make sure that he had a dose of omeprazole daily if he decided that ibuprofen was the better drug in a particular set of circumstances. Omeprazole can be bought from a pharmacy in the UK without a prescription for short courses. John would have to prescribe it for long term use.
Moderate to Severe pain
If severe pain is likely to occur for a short duration - perhaps due to having a procedure done, or cleaning and stitching a wound in a particularly sensitive area, local anaesthetics or even nerve blocks can be very effective.
When paracetamol or ibuprofen on their own are not enough to deal with a particular longer-term pain, the next step is to add in a small dose of codeine.
Codeine on its own cannot be obtained in the UK without a prescription, but it can be bought, at low dose, in combination products with paracetamol (co-codamol) or ibuprofen (Nurofen-Plus) from a pharmacy.
Codeine is a member of the opiate family and acts by activating receptors in the spinal cord and brain to cause analgesia, sedation, nausea, itching, euphoria and to suppress breathing. The additional site of action greatly increases the overall effectiveness of the analgesia.
The receptors are also present in the gut and act to stop the rhythmic squeezing which forces the contents towards the anus, resulting in constipation.
Most of these effects (analgesia, sedation, nausea, euphoria and suppressed breathing) reduce over time with continued use. The term is tolerance.
Constipation is not one of the things the body becomes tolerant to and will be an issue if codeine is taken for longer than a day. All humans and probably all humanoid aliens (sorry Loki or Thor) will be affected!
If pain is due to muscle spasm, then another group of drugs may be considered specifically to treat that. Diazepam is effective as a muscle relaxant, but causes drowsiness at the start of treatment and is extremely addictive, so is not available without a prescription. It would not be prescribed for more than 3 days at a time.
As Sherlock is an addict, I would not like to see him given diazepam unless there was absolutely no alternative. He would become addicted to it more easily than most non-addicts.
Anyway – there is plenty of scope for John to give Sherlock therapeutic massages (!) if he has episodes of muscle spasm.
If low-dose-codeine combination preparations are insufficient, we have to move on to prescription drugs.
A high dose codeine with paracetamol combination is the most commonly used (co-codamol 30/500). It is only the codeine dose that is increased – the paracetamol dose is already at it’s maximum.
The alternative oral formulation for people who really cannot tolerate codeine is tramadol.
Vicodin is NOT AVAILABLE in the UK.
Co-codamol 30/500 or tramadol are strong enough to treat the pain associated with most surgery after the first 24 hours. Ibuprofen or a stronger NSAID can be added for their anti-inflammatory effect. Using a NSAID often reduces the amount of opiate needed to achieve pain relief.
Don’t forget the laxative, the anti-nauseant and the omeprazole (unless you want to torture your patient!)
Injectable opiates are used when a patient is not taking anything orally, due to surgery, for example, or if the analgesia needs to kick in immediately, before an oral dose will work. They are not otherwise appropriate for the type of patient we might see in a James Bond or Sherlock Holmes story – unless you are writing about palliative care at the very end of life.
Single doses for painful procedures are likely to be morphine. If an infusion is being given over a period of time, for example after surgery, then diamorphine is more likely to be used in the UK as it is more soluble and can go in a syringe driver for patient-controlled analgesia.
Treatment of Pain in drug addicts
Some people would consider Sherlock to be a special case because he is an addict.
Perception of pain is increased in opiate addicts (heroin in his case), while they are taking their drug of choice and also for at least a month after they have stopped.
Added to this, addicts, and anyone who legally takes opiates chronically, become tolerant to the effects of the whole group of drugs such that increasing doses are required to achieve the same effect in terms of both pain relief and euphoria.
Therefore, Sherlock’s genuine requirements for pain relief will depend on where he is in the cycle of addiction at a moment in time.
A patient being an addict is no reason to deny appropriate pain relief by giving opiates if they are necessary, but does mean that getting the doses right and stopping the drug in a timely fashion to avoid relapse is more difficult than in a non-addict. Local anaesthetics are particularly useful as they can totally numb an area for a short period of time.
When Sherlock was shot by Mary and had his operations to repair the damage he would have received morphine (or most likely diamorphine in the UK) through a patient controlled activation (PCA) pump attached to the drip stand next to his bed – allowing him to control what he received up to a pre-set maximum. There was no indication that he had recently taken illegal heroin, assuming that the relapse after John’s wedding was several months before the shooting, so his pain perception should have been more or less normal.
The medical staff including John and presumably Sherlock himself would have been keen to stop the opiate as soon as possible, so he would probably have been prescribed one of the stronger non-steroidal anti-inflammatory agents along with regular paracetamol to provide as much opiate-free analgesia as possible after he left hospital. John would have had access to stronger drugs such as codeine or tramadol if they were found to be necessary.