Medicinal herbs are a semi-uncommon resource with currently very few uses.
While a bit of a cheat, a great source of herbs is by doing Sylvia Bluth's side mission in Downtown Santa Rosa (keep in mind she is not always there). During this side mission all medical zombies and containers in and around the nearby store will have greatly increased odds of dropping antibiotics (average quality). You can then drop or salvage these in your inventory to prevent finishing the quest (as this will decrease the collection counter) until you have all the herbs you need.
Research projects - random values
- Laboratory - 25
- Homemade remedy - 4
- During beta, there used to be two medical resources, with the second being "Powdered medicine". It never had an icon, and after removal all the items that gave it as a resource now give medicinal herbs.