Brian123
I am still not convinced with the or/and split. I understand the use of both, but shouldn't we be using and in a list like this?
You are right to be unconvinced -- "or" is wrong here, and "and" is correct (despite what the "OE" claims). I replied in this thread years ago, but my post was so long I'm guessing many people didn't read it, which is understandable.

To see why "and" is correct here, compare these two sentences:
The new Water Act bans lead, mercury, and phosphates.The new Water Act bans lead, mercury, or phosphates."And" is clearly correct if the sentence means "all three of these things are banned". "Or" conveys the bizarre meaning "one of these things is banned but I'm not telling you which".
Sometimes when we use "and" we create a single semantic unit, which creates some situations that superficially appear to contradict the above. These two sentences create a different meaning, as the verb conjugation indicates:
Drinking and bowling is prohibited after 8pm. (you can't simultaneously drink and bowl after 8pm; here "drinking and bowling" is a single semantic unit, as the singular verb indicates)
Drinking and bowling are prohibited after 8pm. (you can't drink after 8pm, and you can't bowl after 8pm; here "drinking and bowling" are two separate activities, as the plural verb indicates)
If we reorder the words above, the meaning can become ambiguous: it's not clear what
After 8pm, the rules prohibit drinking and bowling means, because without a singular or plural verb, it's no longer clear whether "drinking and bowling" is a list of two unrelated things, or if it's a single semantic unit. In this case, if we want to indicate that it's a list of two unrelated things, we often would use "or" instead of "and" (
After 8pm, the rules prohibit drinking or bowling) even though this risks conveying the 'bizarre meaning' I mentioned above.
But that consideration is irrelevant to the problem in this thread, since the list in the original question is clearly not a single semantic unit. There is only one logically correct conjunction here. That said, I can't imagine the GMAT ever testing this issue, so it's probably not important.
I'd add that some of the replies above are incorrectly interpreting the meaning of "illegal drugs" in this sentence. That phrase means something like "narcotics" here. The "steroids" and "growth hormone" earlier in the sentence are not examples of "illegal drugs".