I'm a Ph.D candidate in pharmacology who is applying to med school this year. Can you expand on your interest in pharmacology? Some (most? I know mine did) schools have undergrad courses in it you can take that will familiarize you with basic concepts such as receptor theory, DMPK, and mechanisms of drug action. I would start off with one of these to see if you like the subject matter. You will definitely want to have taken cell biology as a pre-requisite and organic chemistry would probably be helpful as well
If you still like pharmacology after taking such a course, you could consider doing research in the field. Pharmacology research can take a wide variety of forms. Some labs do drug discovery, where they look to identify and optimize new drugs using biochemical assays and chemical synthesis. Some labs try to identify new uses for drugs that have already been developed to improve the standard of care for patients. Other labs focus entirely on cell signaling/physiology. I would read about the research opportunities available to you and contact the PI in charge of the lab if you're interested in undergraduate research. Your university probably has a specific program for this that you can take advantage of. If not, look for summer research programs at schools with prestigious pharmacology departments.