First of all, the reason I'm asking this is because I'd just done an experiment detecting MDMA in a urine sample with GC-MS for my internship program. I'm having difficulties figuring the functional group which cause the said effect as in my question. I've read two journal Shulgin and Nichols and I thought they explored more of the hallucinogen effect from N-methylation.
Firstly, MDMA is widely regarded not to be physically addictive, which simply means that the compound (actually the absence thereof) will not cause potentially life-threatening symptoms on discontinuation, as is the case with alcohol or morphine. Note however that this does not make any statement on the addictive potential of the substance, as e.g. cocaine also falls into this category of substances, which are called psychologically addictive.
In general psychological addiction (which is not necissarily associated to substances, but can also involve habits such as gambling or eating) is widely believed to be strongly associated with the dopamine system and the overstimulation that dopamine facilitates during the addictive actions.
Which brings me to the second point: The active site of the molecule. In a way, looking at both structures you will notice a set of similarity between dopamine and MDMA. It is not that simple however. The effects of MDMA are quite complicated and due to its status as illegal substance research is kind of limited.
Known effects are:
- Known and experimentally confirmed increase in dopamine levels, although the mechanism is not known.
- Serotonine release from vesicles to synaptic cleft (has effects on dopamine levels through mediation/coupling)
- MAO inhibition (decreases dopamine and serotonine degradiation - among others)
Other effects like oxytocin response are also proposed and may also have effect on dopamine levels. But in this case the effect could as well be a down-regulation.
Which structural component is responsible for all of this? All of them, as you can tell from the complexity of the physiological reaction on the substance, especially if compared to similar compounds with in some regards drastically different physiological effects. Think of (meth-)amphetamine(very high dopamine response, next to no serotonin effects) or mescaline(direct agonist on specific serotonin and dopamine receptors, as well as dopaminergic effects). (It would really blow the reach of this question, but taking a look at other compounds, such as 2-CB or 3,4-CTMP will make this picture even more complicated, but also more complete...)
These substances can give you at least some hints at two honorable mentions in terms of 'addiction-causing functional group':
- 3,4-(+M)-substitution pattern on the aromatic ring
A small sidenote on the difference between physical and psychological addiction: I am not 100% sure about the current research in that topic, but afaik in both cases there is in overexpression of receptors that causes the addiction, only that in the case of a psychological addiction the effects of the receptor-agonist is not live-threatening. In that sense the terminology which kind of suggests that psychological addiction is not associated with any changes in brain structure is somewhat misleading.
It's not really any particular functional group that causes addiction. For example, the only functional group in ethanol is the alcohol. While mdma has a methylene dioxy group and an alkyl amine.
Both of the above mentioned drugs are addictive. And their addictiveness can be associated to biochemical changes in the body. Such as the over/under expression of certain genes.