Rules about using medications in a game should cover both how to calculate a dose correctly and what happens if your apothecary or party healer gets it wrong.

Four years ago, Eris Lis, M.D., began writing a series of brilliant and informative posts on RPGs through the eyes of a medical professional. Following is the second of them, which appeared here on December 15, 2012.

As work continues on the revised version of Insults & Injuries, the fastest-growing chapter remains that on medications. The medications chapter is fun to work on because it takes some of the same principles (and substances) as the chapters on drugs and poisons and looks at them from a slightly different point of view. In practice, this has meant changing the way the material is presented and even including a couple of additional game mechanics, including how to calculate a dose correctly and what happens if your apothecary or party healer gets it wrong.

Any time that a creature wishes to administer a medicine in an appropriate amount, the creature must make a Heal check at a difficulty determined by the substance's "therapeutic window," meaning, how wide the safe margin of error is when calculating how much to take. This Heal check is made by the creature calculating the dose and at the time that the dose is prepared, and not by the ingesting creature at the time of use. A creature may take 10 or take 20 on this check presuming the creature has sufficient time and is not prevented from focusing. A creature with Craft (Alchemy) may instead use that skill, in which case the DC is considered to be 5 higher.

If the Heal check succeeds, the dose has been calculated correctly. The medication has its intended effect.

If the Heal check fails by 10 or less, the dose has been under-estimated. The creature ingesting the medicine experiences all of the side-effects but does not receive the full benefits. See each medicine's description for details.

If the Heal check fails by 11 or more, the dose has been over-estimated. The creature ingesting the medicine overdoses. See each medication's description for details.

This week, here's a sneak preview of how these changes are shaping up, by comparing how the same drug, opium, appears in the chapter on illicit drugs versus the chapter on medicines.

Opium (Recreational)

Also known as: Poppy tears, juice of forgetfulness, gods’ medicine

Description: Opium is a drug produced by drying the sap-like fluid (“latex”) that comes from the opium poppy. When the fruit of the poppy is cut, a thick white fluid leaks out, which dries to a brown residue, opium, and can be collected. Opium has been used by herbalists and alchemists since before the invention of writing, and it is the most potent non-magical pain relief known to the civilized races. Opium is often ingested, either as a resin or compressed into a pill-like shape. Healers wishing to use opium as an anesthetic commonly mix it into wine, obtaining the benefits of both the opium and the alcohol.

Recreational use of opium is rare. In areas where the plant is grown, illicit use is uncommon, and in areas where the plant is rare and use as a drug is more common, the exorbitant cost of opium tends to restrict its availability. The practice of smoking opium is relatively new and dates back only a few hundred years. The actual opium is not burned; when the resin is heated, the vapors released contain most of the drug, and this vapor is inhaled.

Whether ingested, drunk, or smoked, opium dulls pain and reaction to pain and induces feelings of euphoria. Side effects of opium include depressing the lungs, potentially stopping breathing.

Mechanics: A creature who ingests opium in recreational doses experiences reduced pain for 1d4x30 minutes. During this time, the creature receives a +4 bonus to saves versus fear effects and a +6 bonus to Concentration checks due to pain (e.g. spellcasting despite taking damage), and all nonlethal damage taken is halved. Spells that exert their effects through pain (such as a Symbol of Pain) or sadness (such as Crushing Despair) impose only half of their usual penalty.

A creature trying to calculate an optimal recreational dose of opium must succeed on a Heal check (DC 15). If this check fails, the dosage is too low and the drug’s user is affected for one half the drug’s normal duration. If the check is a critical failure, the dose is too high. The creature falls unconscious for 2d4x30 minutes. The drug’s user must make a Fortitude save (DC 15) at the time the drug is ingested and again after one hour. If both saves fail, the creature ceases to breathe and suffocates.

Treatment: Delay Poison and Neutralize Poison affect opium normally, immediately ending all effects, awakening an unconscious creature, and restoring breathing to normal in case of an overdose.

The Heal skill may be used in place of a poisoned creature’s Fortitude check in the case of overdose only; success prevents suffocation but does not awaken the creature until the drug’s duration elapses.

Opium (Medical)

Also known as: Poppy tears, juice of forgetfulness, gods’ medicine

Description: See Chapter 6: Drugs and Toxins.

Mechanics: A creature may calculate a dose of opium as a moderate dose to act as a pain-killer (analgesic) or at a high dose to cause unconsciousness (anesthetic). Opium takes effect after 1d10 minutes.

At analgesic doses, the creature who ingests opium experiences reduced pain for 1d4x30 minutes. During this time, the creature receives a +4 bonus to saves versus fear effects and a +6 bonus to Concentration checks due to pain (e.g. spellcasting despite taking damage), and all nonlethal damage taken is halved. Spells that exert their effects through pain (such as a Symbol of Pain) or sadness (such as Crushing Despair) impose only half of their usual penalty.

A creature who ingests an anesthetic dose becomes asleep and Helpless for 1d6x30 minutes. The creature cannot be awakened by painful stimuli.

Side Effects: Constipation. This has no in-game effects but can certainly ruin a creature's day.

Dose DC: 25

Underdose: The creature is affected for one half the drug’s normal duration.

Overdose: The creature falls unconscious for 2d4x30 minutes. The creature must make a Fortitude save (DC 15) at the time the drug is ingested and again after one hour. If both saves fail, the creature ceases to breathe and suffocates.

Treatment: Delay Poison and Neutralize Poison affect opium normally, immediately ending all effects, awakening an anesthetized creature, and restoring breathing to normal in case of an overdose.

The Heal skill may be used in place of a poisoned creature’s Fortitude check in the case of overdose only; success prevents suffocation but does not awaken the creature until the drug’s duration elapses.