Red Herb

Fixed spots: - Leon: 1-2 Campus (2: the optional classroom and the tables by the Campus Keycard gate); 1-5 Gun Shop (upstairs, left of the door); 2-2 (Helena's route, coffin with a lid); 2-4 (far toilet of the restroom); 4-3 (back room of the fish store); 4-5 Train (3rd carriage, left); 5-1 Port Area (the gas room, at the back by the counter; timed). - Chris: 2-1 (up the stairs by the machine-gun tower); 2-3 (underground passage); 2-4 City Hall (room on the right before you meet "Ada"); 3-3 (after Iluzija, when Marco boosts you up); 3-4 (1st room of the floating restaurant). - Jake: 1-2 (Sherry only, above the restroom); 1-3 (behind a crate); 1-4 (passage); 2-1 (slide tunnel); 3-2. - Ada: Ada Chapter 1 (by the projector in the briefing room); Ada Chapter 4 (4-3).

Useless on its own. Mix it with a Green Herb: Green + Red = 6 Health Tablets, the best mix in the game. Keep it until you have a Green.

Green Herb + Red Herb

There is no Red + Red mix. One wiki page gives Green + Green + Red = 12 tablets, but it contradicts the official manual: do not count on it.