I think that it's an interesting addition to a world, but could use some refinement. I'd focus on three things: adding flavor and color to the drug beyond the pure mechanical effects of it, refining the addiction mechanism, defining what the drug does to an existing magic user, and defining how the drug influences the world.
Flavor: how to roleplay a drug user
I think it may be worth defining some additional psychological effects of the drug. Does it feel like the user has a deeper connection to the mysteries of the universe, or is it a power rush that makes the user feel invincible? Describing to the player how their character feels when they use this may help with immersion into the game, and could better reflect exactly why this drug is addictive.
This applies both to using the drug and to withdrawal from the drug. If a player feels weak and powerless, that's a good hook to using more of the drug, if they're willing to roleplay it.
There could also be an associated mechanism to reflect these changes. Perhaps the player receives a boost to their charisma and a penalty to their wisdom to reflect the massive boost of reckless energy they gain. Perhaps they receive a boost to their wisdom and penalties to intelligence and charisma to represent the zen-like trance they enter.
The mechanics of addiction
Rarely are real-life drugs as simple as "do this drug and get addicted.** If they were, people wouldn't do them. If you drug has an effect of "you probably won't get addicted the first time," or "you might want to use more, but the strong-willed can easily quit," addiction isn't as much of a barrier to the first-time user.
Mechanically, this could be represented by a low constitution or will save to resist addiction when using the drug that increases as the player uses more of it. Differing levels of addiction could be represented by how much the player fails a save by. If the effects of using the drug are really nice for an adventuring party, this sort of mechanism could make it far easier for a player to justify "just this once" or "only a little bit" behavior. This is far closer to the pattern of use exhibited by many real world addicts, and also makes it easier for your player to slip into bad habits. What starts as "just this once" can easily become a regular pattern when the players use the drug seemingly without consequence and start to rely on its effects.
How it affects magic users
The drug could also be interesting if it not only grants the ability to use magic, but also boosts the magical prowess of magic users. Additional power could be a hugely tempting reason for mages to use the drug, and could also represent a cultural difference between groups of mages. Perhaps the "good" law-and-order mages find it reprehensible and shun its users (though secretly the grand abbot is hooked on the stuff), while the evil mages venerate its use. Perhaps the law-and-order kingdom publicly bans and reviles it, but recognizes that it can give its mages an edge in battle and supplies the army with the drug.
How it affects the world
A lot of these sorts of flavor effects will affect the world and how different groups see the drug and drug users. In an area with few magic users, drug use could offer the only means of resisting powerful foes. In poor communities, drug use could offer enough magical power to break the cycle of poverty. Perhaps using the drug just feels really good and there's a black market for that purpose, just like in the real world.
Especially if this drug isn't a new thing, there's likely to be built-up attitudes of permissiveness and revulsion associated with drug use that differ in different communities. The more you can weave a compelling narrative integrating this drug into the world, the more your players will buy into the story that surrounds it.