Monday, August 13, 2007

What is addictive about smoking?

The story I have long believed is that it is nicotine that addicts smokers to tobacco products but that it is the other compounds in tobacco (e.g. tobacco specific nitrosamines) which cause medical problems such as cancer.

Hence one way to encourage people to stop smoking is to provide NRTs (nicotine replacement therapies) such as nicotine patches, gums, nasal sprays or inhalers to deal with the chemical dependence and, by so doing, eliminate the ingestion of other health-damaging compounds from cigarette smoke. The idea is to use NRTs to break the physical dependence of nicotine as the smoker breaks the behavioural cues that trigger smoking.

In fact these sorts of pharmaceutical interventions have been tried often without a great deal of success (Balfour and Fagerstrom). The reasons are various – the NRTs may be inappropriately used, may release nicotine to the brain too slowly or be used by low-intensity smokers who are smoking-dependent but not dependent on nicotine.

There are in fact over 4000 chemicals in cigarette smoke many of which could potentially contribute to dependence on tobacco. The consensus has been that nicotine is the major component of tobacco responsible for addiction.

Commenter ‘dany le roux’ suggested (in remarks on an earlier post) that nicotine may not be the only addicting agent when tobacco is smoked. Nicotine definitely seems to be a major addicting agent through its action on nicotinic acetylcholine receptors and the downstream release of dopamine. However non-nicotinic components of tobacco smoke may also play a role by inhibiting monoamine oxidase (MAO) activity and subsequently altering neurotransmitter levels – this might enhance the addictiveness of nicotine by providing anti-depressant effects.

As I understand it dopamine releases can be stimulated in the brain directly by nicotine or other chemicals may inhibit the action of those chemicals which destroy dopamine. It is conjectured that both processes go on when cigarette smoke is ingested. A simple discussion is here.

A survey of recent research in this area is provided in the survey article by A. Lewis, J.H. Miller & R.A. Lea. Understanding these issues may lead to more effective pharmacotherapies for smoking cessation that utilise these MAO inhibitors. Several MAO inhibitors have already been trialled – these are discussed in the Lewis et al. paper.

The issue of policy importance here is that it may be fallacious to put all weight on NRTs as a cessation therapy. They have not performed that well to date perhaps for the reasons discussed above. It would be interesting to find out whether 'smokeless tobacco' products such as snus outperformed NRTs in delivering MAO inhibitors or if these products are only delivered by smoke.

I’ll keep a watchout on this literature – thanks to dany for the tip on MAOs.


rabee said...

I smoked for a long time. I gave up a number of times and it was very difficult.

In 2001 I started using NRT (gum). The transition from cigarets to gum was very smooth.

Two months ago I gave up the gum. It was far more difficult than giving up cigarets. The addiction is similar (you need gum every hour or so) but the reaction to giving up is a bit different.

With cigarets it was quick sharp agony lasting five or six days, while with gum it was prolonged agony that lasted eight weeks.

Francis Xavier Holden said...

I smoked reasonably heavily at times, pack of camel a day, but gave up for years at a time with very little effort. Even now I'm happy to smoke socially, say 10 or so at a BBQ or bar, but then go weeks without a drag.

I seem to have virtually no addiction to nicotine, as patches etc seem to have little or no effect. Others I know need to be on patches or NRT for years.

I seem to remember research which pointed to nicotine dependency being indicated by the regularity with which a smoke was needed - eg if a person must have a smoke every 20 minutes or so - pretty much on the dot.

With me it seems to have been a social and fiddling with the hands and mouth stuff. I would get more pleasure out of say a rolly than a tailor made and lots of fun from fiddling with a pipe.

(as a side issue why have pipes become so unfashionable - is it the trend toward minaturisation, like mobiles or ipods, where a huge pipe the size of a wood fired heater, sticking out the mouth belching industrial quantities of smoke, ash and other pollutants like a Vesuvious).

perry said...

This problem lies in the tragic addiction of various govt's to those billions of dollars of tobacco taxes. If shops were forced by law to stop selling tobacco, very few people would be able to continue the habit.

hc said...

fxh, You are in a minority but there are 'chippers' like you. I found S. Shiffman et al (Smoking Behaviour and Smoking History of Tobacco Chippers, Experimental and Clinical Psychopharmacology, 2, 2, 1994, 126-142) interesting. You sound like what they call a 'converted chipper'. You are like a 'social drinker' except that with alcohol most fall into this category but with smoking few do. You presumably gave up a nicotine dependence but could continue smoking at low levels or never was chemically addicted to smoking.

Of course N.E. Zinberg, Drug, Set and Setting pointed out this behaviour with respect to heroin use.

Anonymous said...

Not that I understand the purpose of the other 500 chemicals added to my tobacco; but just curious, does anyone know why valine would be added to cigerettes?

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