The three substances addressed by Relapsd-nicotine, cannabis, and alcohol-have completely different molecular targets. Nicotine binds to nAChRs. THC binds to CB1 receptors. Alcohol modulates GABA-A and NMDA. Yet they all produce addiction through the same final common pathway: the mesolimbic dopamine system.
The Circuit
The mesolimbic dopamine system runs from the ventral tegmental area (VTA) in the brainstem to the nucleus accumbens (NAc) in the ventral striatum, with projections to the prefrontal cortex, amygdala, and hippocampus.
The VTA contains the cell bodies of dopamine neurons. The NAc is the primary site of dopamine release in response to rewarding stimuli. The prefrontal cortex receives dopamine input that modulates decision-making and impulse control. The amygdala and hippocampus encode the emotional and memory components of reward.
This circuit evolved to signal reward-food, sex, social connection-and motivate behavior toward those rewards. A well-functioning mesolimbic system says "this was good, do it again" in response to evolutionarily adaptive behaviors.
How Drugs Hijack the Circuit
Nicotine: Binds to α4β2 nAChRs in the VTA → directly activates VTA dopamine neurons → dopamine surge in the NAc (200% above baseline)
THC: Binds to CB1 receptors on GABAergic interneurons in the VTA → removes inhibitory tone from VTA dopamine neurons (disinhibition) → dopamine surge in the NAc
Alcohol: Activates GABA-A receptors (inhibiting inhibitory interneurons in VTA) AND inhibits NMDA receptors → disinhibits VTA dopamine neurons → dopamine surge in the NAc
Different entry points. Identical output: dopamine flooding the nucleus accumbens.
The Craving Memory
The amygdala and hippocampus record the context of each dopamine surge. Over time, the contextual cues associated with drug use (a particular location, time of day, emotional state, social context) become capable of triggering dopamine release in anticipation of the drug-before any drug has been consumed.
This is the mechanism of craving. A craving is a conditioned dopamine anticipation response, not simply a desire for the drug's pharmacological effect.
Why Withdrawal Is Negative
With chronic drug use, the mesolimbic system adapts to the artificially elevated dopamine. Baseline dopamine falls. Hedonic set point decreases. Normal rewards become less rewarding.
Withdrawal is not just the absence of the drug's effect. It is the presence of a below-normal dopamine state-anhedonia, reduced motivation, dysphoria-that the drug reliably reverses.
Why They're All Different Despite Using the Same System
The fact that all addictive drugs converge on the mesolimbic dopamine system does not mean withdrawal is identical. The upstream mechanisms differ completely:
- Nicotine withdrawal involves nAChR upregulation and cholinergic dysregulation
- Cannabis withdrawal involves ECS dysfunction across sleep, appetite, mood, and stress
- Alcohol withdrawal involves GABA-A/NMDA imbalance with potential for physical danger
These upstream differences determine the character, severity, and appropriate intervention for each withdrawal. Understanding both the common pathway (mesolimbic dopamine) and the substance-specific mechanisms is the foundation of the Relapsd approach.