Mage Powder  from  Jeffrey Adams.

                              Here’s a really sick and twisted magical item I came up with. Mage powder. It can be
                          inhaled or swallowed (if mixed with a drink). Inhaling it has double the effects. It affects
                          a mage (only, others feel nothing other than a slight tingling) as follows:
                               Each dose adds 1d6 points to intelligence. They dissipate at 1 point per hour. While
                          intelligence is raised, the mage can memorize more spells, make better saves, etc as
                          though his intelligence were permenantly at that level.
                               Once intelligence returns to normal, it CONTINUES TO DROP until it reaches 1/2
                          the points below normal (I.E. if the mage rolled a 6, and had a 12 int, it would go up to
                          18, then over the course of 9 hours it would drop 3 points below normal, to 9). For
                          every hour after that, INT goes back up 1 point until it’s back at normal.

                               Also, with every dose the mage must roll a CON check with a penalty equal to the roll
                          (the above mage would make a con check with a 6 point penalty). If the mage fails,
                          he’s addicted to the mage powder.

                               Once addicted, things become much worse. Every time INT drops below normal, it
                          will only rise to one point less than normal before (I.E. after 3 uses, our 12-int mage
                          would have an effective int of 9). Also, with every use the mage makes another CON
                          check, and every time he fails his CON goes down by one point. Also, the addiction
                          makes the mage desire more powder the longer he goes without, I don’t remember
                          exactly what the rolls were, but after a certain period he WILL ingest more powder if
                          he’s got any within reach.

                               Once INT ever reaches 0, the mage falls into a coma, with CON decreasing 1 point
                          per day until the mage dies. The mage can be woken with clerical help, and he can
                          break the addiction, but it requires a lot... If he can be held without access to mage
                          powder for a number of weeks equal to the difference in his CON (original con is 10,
                          current con from addiction is 6, must be held for 4 weeks) he’ll break the addiction if
                          he makes a system shock check. Each day he is waiting, he takes 1d12 points of
                          damage from withdrawal symptoms (in other words, he better be really tough, or in the
                          care of a cleric while going through withdrawal). If he fails the check, he’s still addicted
                          and must wait longer, making a check each week until the addiction is broken. CON
                          and INT then go back up at the rate of 1 point per day spent resting.

                               Of course, your mage(s) will have to find out about the addiction the hard way... <evil
                          grin>. You should have seen the look of horror on my mage’s face when his INT first
                          dropped below normal. Using this is pretty good just as an adventure in itself, since by
                          the time your mage needs help from the rest of the party he’s probably pretty bad off.