I understand the low-level pharmacodynamics (but these are seldom useful when talking about high-level, system-wide, and complex effects).
BUT, this portion https://en.wikipedia.org/wiki/Nicotine#Reinforcement_disorde... has a few interesting tid-bits, especially the article on DeltaFosB/"as a critical factor in the development of virtually all forms of behavioral and drug addictions." (https://en.wikipedia.org/wiki/FOSB#Delta_FosB) As well as, "Based upon the accumulated evidence, a medical review from late 2014 argued that accumbal ΔFosB expression can be used as an addiction biomarker and that the degree of accumbal ΔFosB induction by a drug is a metric for how addictive it is relative to others."
Fascinating stuff -- and exactly what I was complaining about.
A more nuanced take on why drug-mediated DeltaFosB expression may be involved in addictive (see: habitual drug usage) behaviors: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2607320/
BUT, so many things cause DeltaFosB expression (e.g. sugar, exercise, drugs, etc.), that we need to establish how significant of an effect nicotine has compared to everything else. Fortunately, we do have one study comparing caffeine's and nicotine's DeltaFosB expression: https://sci-hub.se/10.1016/j.jchemneu.2017.10.005
Results (page 9; "number of DeltaFosB-immunoreactive nuclei per 1 mm^2" in the nucleus accumbunus):
| Control | Nicotine | Caffeine |
| 43,83 ± 16,80 | 117,33 ± 14,36 | 112,77 ± 10,12 |
To me, that looks like a similar addiction-profile. Granted, DeltaFosB is probably not the be-all end-all, but a small piece in untangling why and how nicotine (and other drugs) may or may not be addictive.
It would be even better, if we could put these two side-by-side with other drugs, notably cocaine and heroin, to see if the effect expression is logarithmic (and DeltaFosB over-expression is similar across-the-board for all drugs considered addictive).
