According to David Dryer (the film's Effects Supervisor), the pill she is swallowing is in fact a **birth control pill**:

> Scott's intentions with this imagery, as related by special effects
> supervisor, David Dryer, are revealing; *"What happened... was that
> Ridley and I had a meeting where he told me,'I want a bunch of phony
> oriental commercials where geisha girls are doing unhealthy things.
> Smoking, taking drugs or whatever. To kind of continue with the
> oppressive feeling throughout the landscape"*. **Dryer
> also reveals the idea he had for the type of pills the geisha is seen
> to be swallowing, namely, birth control pills: *"This was strictly my
> idea - it seemed to make sense that birth control would be heavily
> advertised in such an overpopulated future".*** <sub><sup>[Berliner Chic][1]</sub></sup>

[IMDb][2] also identifies the line that is playing:
> In the strange Japanese advertisement shown on the side of a blimp, in
> which a Geisha-like woman is swallowing a pill, the loud speakers play
> a line from a Japanese Noh play, saying "*Iri Hi Katamuku*," literally
> "*the setting sun sinks down*."

For completeness, I'd like to mention that the advert itself is considered to be a parody of an existing Japanese product; [Strong Wakamoto][3]. A yeast-based pill that supposedly keeps you (ahem) regular.

  [1]: https://books.google.co.uk/books?id=-X6Y4W62sF0C&pg=PA147&lpg=PA147&dq=%22David%20Dryer%22%20and%20%22birth%20control%22%20and%20geisha&source=bl&ots=qDJWK3Kypd&sig=DSXOfzMsIHAR18FRQ-7XIGEdFDk&hl=en&sa=X&ei=9NG_VJHSHMnuUr2mhJAL&ved=0CCYQ6AEwAQ#v=onepage&q=%22David%20Dryer%22%20and%20%22birth%20control%22%20and%20geisha&f=false
  [2]: http://www.imdb.com/title/tt0083658/trivia?item=tr0753873
  [3]: https://www.wakamoto-pharm.co.jp/english/product/index.html