Hi there. I'm setting this as a five dollar answer -- but if you think
it needs more time, (and therefore more $) please let me know. My
question, which relates to a piece of fiction I'm working on, is as
follows: was either morphine or codeine administered orally (and esp.
in pill form) as a pain killer in the U.S. between the years of 1915
and 1925? If so, can you find some documentation? And if not, can you
help me to find other habit-forming oral (and ideally pill form)
anesthetics that might have been used during that time? For my
purposes, this anesthetic need not have been used extensively, but
must have been available to a physician in the western US circa 1920.

How about Cocaine?

http://www.findarticles.com/cf_dls/m2005/2_35/82066768/p1/article.jhtml

I suggest that codeine is your best choice. It has been widely
available since the mid-19th century, is commonly prescribed in tablet
form, and is (like all opiates) addictive.

Morphine loses potency when taken orally, and thus is less likely to
be taken in tablet form.

Note that these drugs are not anesthetics, but analgesics.

You might have look at butalbital (Fiorinal) which has been around
since the '20s.  It *can* be habit-forming but has no addictive
properties; it's more in a dependency category.

http://www.headachedrugs.com/archives/butalbital.html

Another possibility is heroin (diamorphine). Long before it became a
"street drug," heroin was a pharmaceutical product. It was dispensed
in liquid form (for injection) and as tablets.

Here's an ad for Bayer products, including heroin:

http://www.a1b2c3.com/drugs/opi004.htm

In regards to morphine and codeine, they are both ANALGESICS and NOT ANESTHETICS.  

An analgesic is a compound that relieves pain by altering perception
of nociceptive stimuli without procucing anesthesis or loss of
consciousness.

An anesthetic is a compound that reversibly depresses neuronal
function, producing a loss of ability to perceive pain and/or other
sensations.

I assume you are looking for an addictive analgesic and not an
addictive anesthetic.  If you are in fact looking for an addictive
anesthetic, you may want to visit the following site -
http://medhist.ac.uk/browse/mesh/C0002903L0002903.html - it provides
links to many other sites documenting the history of anesthesia.

-d

Thanks, to all, for your help. And thanks to pinkfreud and njbagel for
correcting my faulty terminology.

For what it's worth, Cocaine is reported as having been the first
Local Anaesthetic:

The first local anaesthetic

Dr Adrian Pearce of Guy?s Hospital will discuss the discovery of
cocaine as the first local anaesthetic. 'The local anaesthetic action
of cocaine was first noticed by Dr Karl Koller, an eye surgeon in
1884. Soon it was being used for other types of surgery by injection
into the tissues, around nerves and into the spinal fluid. Local
anaesthesia with cocaine rapidly became very popular because it
provided painless surgery without the substantial dangers and
unpleasantness of general anaesthetics at that time. However, the
toxic effects of cocaine, particularly after injection of large doses,
became apparent and led to the search for safer.'

http://www.rsm.ac.uk/new/pr140.htm