Hmm, assuming a Trueborn, the addiction check is a BOD+WIL double attribute check, with medtech skill as a bonus, minus the strength of the drug.
Going with clan Mechwarrior minimums that is a BOD of at least 4, and WIL of 5. So a target of 9, say a +2 for medtech skill and you have to roll an 8. An Elemental scraping the bottom of the attribute limit (Bod 5, Will 4) has the same numbers. I believe you can use your Pheontype bonus for those attribute minimums?
So slight over 50-50 chance and climbing rapidly from repeated use. OTOH you can't get a compulsion any higher than the strength of the drug. Would that be the effective strength, limiting a Clan Trueborn to a single -1 TP addiction?
This would limit the damage to something on the level of a smoker. A nasty but common vice in Clan ranks? True AFAICT AtoW doesn't go into the long term effects of chemical addictions, particularly the milder ones like nicotine or alcohol, but in a Trueborn's view if you aren't dead by the time they catch up to you, you have done something very wrong.