Mentats: The fallout equivalent of Methylphenidate, a medication used to treat ADHD and narcolepsy. Chewable tablets that help the user focus and heighten awareness through their senses. The addiction rate is medium-low in most cases, but withdraw effects are considered nasty. Symptoms include moods swings and irritability—anything considered uncharismatic really. Severe withdraw can lead to migraines and, even, paranoia.
Stimpaks: They are a mixture of some kind of stimulant and maybe adrenaline, to fight the lethargy pain brings, with a coagulant and healing accelerant to stop the bleeding and heal wounds quickly. First, there's the sting of the needle, but after the discomfort fades, there's an almost soothing heat that forms in the wounded areas. The effect isn't instantaneous, but it can heal minor wounds within a few hours. Broken bones might take more than one stimpak and a night of restful sleep. The formula itself isn't addictive, but there are cases, though extremely rare, where people have gotten addicted to the sensation that accompanies the healing effects.
Med-X: The fallout equivalent of Morphine. A practical, yet heavy-duty painkiller that is commonly used in small doses. Since it is essentially a narcotic, it will make the user loopy, lethargy is a common symptom in habitual use. Symptoms include itching and euphoria. Habitual use can lead to addiction.