Sorry Anna, corgis do shed and there will not be a medication to stop it. To most easily manage a corgi coat may I suggest that you feed a very high quality food, groom regularly, use a rake or furminator to pull out the loose/dead undercoat. At high shed times give a very warm bath and use a cool air blow dryer.....best done outside as the hair goes everywhere. Doing the above things will help you manage the hair. Part of the corgi mantra.....corgis do shed!

Murphy shed like crazy when we first got him, but a half tablespoon of Omega 3/Omega 6 oil on his food every day has curbed his shedding considerably. Pet supply stores usually sell "reduce shedding" food supplement oils. I opted for the far-less-expensive Smart Balance cooking oil that boasts as much omega 3 & omega 6 as the ones sold as a pet supplement.
Also, we've noticed his amount of shedding is a good indicator of his stress level, so his shedding reduced after the first 2 weeks as he became more comfortable with us an our routine. The day he started obedience training, he shed a lot, but then it went back to a reasonable level a few hours after we got back home.

Thanks for all the advice - much appreciated!!