However, there is no description given to the player about what the effects of those herbs are. In fact: The OD&D equipment list has no explicit explanation to any of the items featured therein (including armor, weapons, steeds, etc.; some you have to track down in other places or books, while weapons in fact have no distinctions from one to another in the original LBBs.) The herbs were copied forward into later edition equipment lists, but still received no explication to the players on their effects.
Let's see if we can piece together the intentions from different sources. Using Wikipedia may give you some clues, but I'd like to narrow down what was on the designer's mind in this regard, if we can.
I think it's the case that in OD&D, only one of those herbs is ever referenced at all (emphasis mine throughout this article):
Vampires cannot abide the smell of garlic, the face of a mirror, or the sight of cross. They will fall back from these if strongly presented. [OD&D Vol-2, p. 10]
So that's something, but the phrase "fall back" is at least a bit ambiguous. Let's skip forward to Gygax's AD&D project, and first check in on the DMG, which conveniently includes "Appendix J: Herbs, Spices, and Medicinal Vegetables". This features a very short, inspirational suggestion of possible uses for about 150 herbal types. Fortunately, the three on the equipment list are included:
Notice that a rather specific usage against a D&D-game monster is included as the last element in each of those suggestions. Now let's turn to the AD&D Monster Manual (which was published earlier, of course) for some more detail. Regarding vampires and garlic:
Vampires recoil from strong garlic, the face of a mirror, or a cross (or several other holy symbols of lawful good) if any of these objects are presented boldly. Note, however, that none of these devices harm or drive the monster off. They do cause a vampire to hesitate 1 to 4 rounds before attacking in the case of garlic... [AD&D MM, p. 99]
While in the entry for lycanthropes (werewolves, at. al.) we see this:
Any humanoid creature bitten by a lycanthrope for damage equal to or greater than 50% of its total potential, but not actually killed (and eaten), is infected by the disease of lycanthropy. If the person is carrying belladonna there is a 25% chance that this will cure the affliction if eaten within one hour. Note that this infusion will incapacitate the person for 1-4 days and there is a 1% chance of the poison in it killing the creature. [AD&D MM, p. 63]
The above is basically repeated in the DMG section on lycanthropy, along with the following tidbit:
If the adventurer decides to be cured and the methods mentioned thus far have been unsuccessful, he or she may take refuge in a holy/unholy place such as a monastery or an abbey. There the clerics can administer to the afflicted one holy/unholy water laced with a goodly amount of wolfsbane and belladonna prepared by the spiritual methods of that particular religion. This potation is to be consumed by the victim at least twice a day from a silver chalice. No adventuring may be done by the character while he or she is being treated by the clerics. After a month or more (depending upon how advanced the disease is) the player character should be cured and somewhat poorer in the purse, as this procedure is very costly. [AD&D DMG, p. 22]
Obviously, this particular usage (of either wolfsbane or belladonna) is of no use to adventurers actively exploring a dungeon. Garlic and belladonna are also mentioned in DMG Appendix O, in the example of encumbrance among the equipment carried by the magic-user Dimwall. The only other reference I can find is in the PHB, where garlic is given as the material component to the spell slow poison.
So while no in-game use for wolvesbane was specified by Gygax, Moldvay in his D&D Basic rules included this:
If a lycanthrope is hit by wolfsbane, it must save vs. Poison or run away in fear. The sprig of wolfsbane must be swung or thrown as a weapon, using normal combat procedures. [Moldvay Basic, p. B38]
I will include one quote from Wikipedia, on the use of wolvesbane in the 1931 Dracula movie from Universal (whose monster movies are clear inspirations in places for the D&D designers):
In the 1931 classic horror film, "Dracula" starring Bela Lugosi as Count Dracula and Helen Chandler as Mina Seward, reference is made in regards to wolfbane (aconitum). Towards the end of the film, "Van Helsing holds up a sprig of wolfbane". Van Helsing educates the nurse protecting Mina from Count Dracula to place sprigs of wolfbane around Mina's neck for protection. Furthermore, he instructs that wolfane is a plant that grows in central Europe. There the natives use it to protect themselves against vampires. As long as the wolfbane is present in Mina's bedroom, she will be safe from Count Dracula. During the night, Count Dracula desires to visit Mina. He appears outside her window in the form of a flying bat. He causes the nurse to become drowsy and when she awakes from his spell, she removes the sprigs of wolfbane placing it in a hallway chest of drawers. With the removal of the wolfbane from Mina's room, Count Dracula mysteriously appears and transport Mina to the dungeon of the castle. [Wikipedia: Aconitum; link]
In this respect, note the otherwise odd language in Gygax's OD&D writeup of the vampire:
These monsters are properly of the "Undead" class rather than Lycanthropes. [OD&D Vol-2, p. 9]
Perhaps this argument is mostly in regards to the movie use of "wolfbane" to ward of the vampire? In the D&D game, Gygax instead specifies garlic, but the effect otherwise seems to be very similar in this respect.
So in summary we seem to find the following intentions for the three special herbs:
- Garlic for warding off vampires.
- Wolfsbane for driving off lycanthropes.
- Belladonna for curing lycanthropy.
Side note: Recently Jon Peterson salvaged and published Craig VanGrasstek's 1974 "Rules to the Game of Dungeon" (link), which apparently documents someone who sat in on a D&D-like game at some point, without ever seeing the D&D rulebooks, and interpolating a set of written rules. One of the things that caught my eye is that in the rather whimsical list of equipment, there are two conspicuous protective items (p. 8):
Notice that there is a neck brace for "safety from vampires", and a special warding device so the "wearer cannot become a were-wolf". No other piece of equipment on this page mentions protections or use against any other specific monster. So from this we can infer that players of the game at its inception were uniquely interested or concerned (for some reason) with protecting themselves from vampires and werewolves. While we don't normally see these exact items, D&D does express the same interest in those two monster types by way of its special herbs in the equipment table (and personally I think it's much preferable to use legendary or real-world content for the same game mechanics).
Back to the main topic. Let's consider how we can clearly communicate the use of D&D's special herbs to the players by way of our maximally-brief house rules.
Herbs, Special: Wreaths of garlic ward off vampire attacks; wolvesbane does so for lycanthropes (save vs. breath negates; –1 reaction checks). Belladonna consumed just after infection may cure lycanthropy (save vs. poison, but on “1” death results).
Notice that you get some protection from wearing a wreath of garlic or wolvesbane, but if your PC does it all the time, then there's a drawback: -1 on reaction checks. What do you think of that? Is it acceptable to make the power of garlic-versus-vampires and wolvesbane-versus-lycanthropes symmetric? Anything else I missed in the published rules?