|Do you know where your variables are?|
Yes. Also, putting in spam filters based on searching for names of drugs and such is a long and boring arms race that only gives you very short periods of "victory" (and often actually just leads to more attention from the spammer since they have to engage in the fight).
The spam that we currently block is spam that is attempted by non-idiots trying to improve their "page rank" in search engines. Excluding the "non-idiots" part, "page rank" spam is the wide majority of spam so far.
What gets through is 1) spam being posted by idiots who don't even realize that they got it wrong and they aren't actually increasing their page rank (and it is sad how much of this there is), and 2) spam doing less-effective SEO nonsense (some of which is actually still being posted by idiots that just don't realize how less effective it is).
In the past, these ineffective spam bouts just fizzled out as the idiot eventually figures out the lack of effect. Some of the time I saw that the fizzle happened when, after posting spam for weeks, they finally noticed that the links in their spam were not rendering properly and so they figured out how to do links correctly and suddenly their spam was no longer posted.
So the thing that should be added to the spam prevention system is not preventing people from mentioning some popular drug name. We need to prevent search engines from seeing any non-approved content from junior members (and non-members). This addresses the less-effective SEO nonsense and also makes the lack of effect more obvious to the more stupid spammers more quickly.
There's also some wrinkles still left to-do for the link filtering features.