Proceed with caution big pharma companies are notoriously litigious.
If you were to wear one of their own branded t-shirts they might object, although I don't know what they could do about it, send you a 'cease and desist' letter? But they could, potentially, argue that you didn't make the distinction clear enough, that you were saying their drugs were harmful to *everyone*, even though you might just want to convey that the side effects affect *some* people, i.e. you. And they could, potentially, try to claim that you damaged their drug brand or their overall brand and want to claim losses from you. Not sure whether they would have a legal leg to stand on, but such legal niceties doesn't usually stop big pharma or any other big corporation for that matter, their legal department and their pockets are bigger and deeper than yours...
There is, however, a tradition of subvertising, e.g. with Coca Cola and the Caterpillar brand and others.
You might be better off trying to design your own t-shirt subvertising the issues you're concerned about.