In game it says it gives 20 attack but when you use it you'll see it's actually 8 attack (as shown on Hidden-Street: http://bbb.hidden-street.net/items/potion/body-and-physics-medicine). I have dropped my Mastery Medicine already but I believe it showed either 25 or 35 magic attack in game, on Hidden-Street it's just 10: http://bbb.hidden-street.net/search_finder/Mastery Medicine I'll also note both of these don't show as untradable but when you drop them they just dissapear (you also don't get the dialogue saying you'll lose them).
Do note that we do tweak the attack values of potions on many other potions (such as Red / Yellow Ciders, Naricain's Demon Elixir) - I wouldn't consider this a bug. The untradeable issue, however, should be revised. Thank you for the report.