The disclosure laws are there for a reason. If you can't satisfy their requirements in a tweet then you can't advertise pharmaceuticals on Twitter. If you can't satisfy them in a Google ad then you can't advertise pharmaceuticals in a Google ad.
This isn't affecting any one company over another or anything like that. It's just following the laws to their conclusion -- and, really, going right along with their intention. Putting a drug in your body is of much greater consequence than what company you buy your mass-produced junk from, and these laws make sure drug companies can't just do snappy, feel-good 10-second spots with no substance whatsoever like beer companies and cola companies.
A big part of advertising is repeating a brand name over and over. There's an impression made by hearing a brand name in association with positive images or text, even if you aren't very involved with the ad. The disclosure laws try to prevent companies from just spamming you with impressions and making sure there is substantial information right up front. If it's behind a link, as many of these companies propose, that's all lost. The casual eye skips over, gets the positive impression and none of the disclosure.
So... within our current framework if there's no room to disclose right up front there should be no ad at all. Maybe the disclosure laws suck, maybe the fact that drugs are advertised at all sucks... those are separate points. As the law stands now, no Twitter ads for Viagra. Yay!