The Chemicals of Addiction
So we all know that nicotine is addictive. But what is not so well known is that research has discovered that many other chemicals can increase addictiveness of a given compound, and that by itself, nicotine is roughly as addictive as caffeine.
This has a baring on how dangerous a substance really is. It doesn't only apply to cigarettes, but it could have a role in why, for example,. junk food appears to be addictive. Many researchers think that fat and sugar is like nicotine in the cigarette, but there appears to be other factors and importantly, combinations of these factors, that drive unhealthy eating behavior, and even more startling, is the possibility that these hidden addicting components in food, cigarettes etc, could have a gateway effect to seemingly very different addictions. For example, a junk food diet has been shown to be related to alcoholism, whilst fresh fruit and vegetables, with different components in them, appear to reduce the addictiveness of alcohol.
Recently, an important discovery was made that showed certain food additives increased the amount of food animals needed to eat and thereby made food more addictive, and this was related to gut inflammation and gut bacteria. See http://www.livescience.com/49949-food-additives-cause-inflammation.html
The mechanism is related to inflammation. Reactive aldehydes in food also can cause this kind of reaction, and guess what, they are also strongly linked to the addictiveness of tobacco smoke.
This research dovetails with the finding that acetaldehyde in cigarettes (and potentially also incorrectly operated e-cigarettes) makes nicotine more addictive. It's possible that similar 'reactive aldehydes' produced by overheated and degraded fats and sugars in our diet could actually prime our brains to be addicted to other chemicals, such as alcohol, nicotine, caffeine and drugs like cocaine, and vice versa by the inhalation of aldehydes in cigarette smoke.
Instead of one gateway-drug, it appears more than plausible that the problem of addiction is caused by multiple gateway enhancing compounds in our diet and a cross-synnergy with stimulants like caffeine, nicotine etc, other chemicals in cigarettes and alcohol. Alcohol too has been suspected to be a gateway drug, and is chemically related to the aldehydes.
Addictive potential of acetaldehyde
Animal studies have shown that acetaldehyde can maintain self-administration behaviour equal to, or probably more effectively than, nicotine (Charles et al. 1983, Philip Morris 1992). Belluzzi et al. (2005) found that acetaldehyde has reinforcing properties (Belluzzi et al. 2005).
And this compound is increasingly suspected to be involved in alcoholism:
More on the nicotine-acetaldehyde link - http://archives.drugabuse.gov/NIDA_Notes/NNVol20N3/Study.html
The scientists conducting this research think that an MAO inhibiting effect of aldehydes is partly responsible. Besides this, cigarettes have other additives in them that are MAO inhibitors, and are known to make nicotine in cigarettes more addictive, it is thought by changing the levels of brain chemicals like noradrenaline and dopamine, both of which involved in addiction behaviors. There are several known groups of such compounds, and they are very powerful:
In addition, it has been shown in several species that nicotine has relatively weak reinforcing properties compared with other addictive drugs. Such a weak reinforcing property cannot explain by itself the intense addictive properties of tobacco smoking, the difficulty most smokers experience in attempting to quit, and the high relapse rates after quitting (Goldberg et al., 1981; Corrigall and Coen, 1989; Donny et al., 1995; Rose and Corrigall, 1997).
Some of this effect may be explained by the presence of certain 'alkaloids' which are plant chemicals that also inhibit human MAO enzymes in tobacco leaf.
So, we can see that addiction could be more complicated than was thought, it likely involves feedbacks from several aspects of lifestyle and combinations of compounds in cigarettes.
In this way, one of the most promising potentials of e-cigarettes would be via the lack of these additional gate-way components. Vaping at a low temperature and preventing dry-wick, will ensure that aldehydes cannot be generated at levels similar to a cigarette. Collectively, switching from tobacco burning to e-liquid delivery of nicotine, holds promise in terms of a graduated withdrawal from tobacco and nicotine addiction, therefore could prove to act as a reverse-gateway towards the full quitting of nicotine in existing smokers, and should prove less dangerous than cigarettes to adolescents.