The chalky red pills manufactured by Med-Tek were a popular recreational (party) drug before the Great War, favored by consumers for their effect on creativity. The active ingredient is a powerful nootropic that increases memory related functions, and speeds other mental processes. Of course, the effect is temporary, leaving the user tired and sluggish once it wears off. Excessive consumption could also result in health complications, including migraines and even debilitating neurological disorders. Coupled with a high addiction rate, Mentats were a double edged sword.
Despite that, chem packages (available both as cardboard packs and tins) sold well, to the point where the company started developing flavored varieties with slightly different properties. Their popularity survived the Great War and made them a popular drug across the wasteland. Some chemists even figured out how to iterate on the design and create special blends of Mentats.
A useful tool for any character build with lower Intelligence, Charisma, and Perception. Mentats can be used by "stupid" characters to converse (if Intelligence is less than 4, the player character is mentally handicapped and cannot speak like a normal person). This allows bypassing some restrictions, such as when talking to Lori at Lost Hills.
Originally in Fallout, Mentats were supposed to be taken intravenously with a syringe: the .frm file for this item still exists in the Fallout Demo files.
Their name is a reference to Frank Herbert's Dune, where, in the wake of humanity rejecting artificially intelligent computers and robots, Mentats are humans trained for computer-like mathematical and logical computations. Additionally, the pills are colored red — red-stained lips are a distinguishing characteristic of a Dune Mentat.
↑Fallout 2 Official Strategies & Secrets p.74: "This party drug was once favored for the boost it gave to creativity—tune in, turn on, drop out. Mentats are just the ticket when you need to figure out something particularly perplexing or impress someone with your wits and charm. Mentats also sharpen your Perception, which greatly enhances long-range sniping attacks."