Yes, in the UK too, anything sold as a medicine must be tested on animals, by law. So it's not like food, where your spending choices affect how much of the practices in question go on. Attempting to boycott drugs for animal testing is useless, as companies will keep testing on animals just as much as now, all the time the law demands it. What we need to do before working on the companies themselves, is to change that law.
Also remember, the fundamentals of our medical knowledge about both humans and animals, come mostly from involuntary tests on both. A lot of what we take for granted was originally discovered by doctors several centuries ago, who paid people to "find" dead bodies for them, some of which were obtained by murder. Then there are all the experiments done in WWII on Jews, Soviet POWs and gay men. A lot of knowledge was obtained from that. Should we pretend we don't know it, or refuse to use drugs that were tested on involuntary subjects, human or non-human, more than several decades ago? Boycotting products that were tested on animals recently, and *not* in order to comply with a law, could have an effect, but medicine, at the moment, I doubt it.