You can get Cure Disease potions in Oblivion (and also cure diseases without them) in a few reliable ways:

Fastest options (no potion needed)

  • Pray at a chapel altar
    • Go to any Great Chapel in a major city (Anvil, Bravil, Chorrol, etc.) and activate the large central altar of the Nine to cure your diseases and restore damaged attributes, as long as your Infamy is not too high.
  • Eat Mandrake Root
    • The ingredient Mandrake Root has a Cure Disease effect when eaten and is commonly recommended as a cheap alternative to potions.
* Plants grow mostly in the western Colovian Highlands, more rarely on the Gold Coast, and around Bravil.

Where to buy Cure Disease potions

  • Imperial City – Market District
    • The Gilded Carafe sells Cure Disease potions and Mandrake Root; it’s an alchemy/ingredient shop even if it doesn’t look obvious at first.
* **The Main Ingredient** near the Arena Gate also sells alchemy supplies and can stock Cure Disease potions.
  • Other alchemy shops
    • Any dedicated alchemy shop in the major cities can stock Cure Disease potions; stock can vary, so you may need to wait 24 hours and check again.

Other ways to cure disease

  • Craft your own potion
    • With a Mortar & Pestle, combine two ingredients that have the Cure Disease property (for example Mandrake plus another Cure Disease ingredient) in the Alchemy menu to brew your own potion.
  • Use a Cure Disease spell
    • There is a Cure Disease Restoration spell (Journeyman level, self) that can be purchased from priests/healers and used instead of potions.

Quick answer: The Gilded Carafe and The Main Ingredient in the Imperial City Market District are the go‑to shops, but altars in chapels and Mandrake Root are usually the easiest cures early on.

Information gathered from public forums or data available on the internet and portrayed here.