Nicotine is a colorless, alkaline, hydroscopic (water-repelling), oily substance that is found in the leaves of a variety plants where it acts as a pesticide against herbivorous animals.

Nicotine is highly poisonous since it acts as a neurotoxin (or nerve agent) in animals. It has been used widely in agriculture as an insecticide due to nicotine's particular toxicity in incests.

In humans, the toxic dose of nicotine is 0.5-1.0 mg/kg of body weight. So for most people between 40 and 60 milligrams of nicotine may prove fatal.

You may be shocked to learn that nicotine is roughly 10 times more toxic than the notorious poison, potassium cyanide, which requires between 5-10 mg/kg to kill.

Nicotine is the most widely abused drug on the planet, with an estimated 1.1 billion addicts worldwide (17% of the world population).

It is now recognized to be such a powerful substance that some people (with a specific gene) can become hooked after smoking only one cigarette. Compare that with the several weeks of use required to become physically dependent on heroin, or months to become hooked on cocaine, and you get the idea of just how potent nicotine is.

Most nicotine users get their fix by smoking the dried and cured leaves of the tobacco plant, and almost all the diseases associated with nicotine use are in fact caused by the other chemicals that are produced by the burning of tobacco.

Nicotine itself has been viewed by researchers as being comparatively safe, but this is only in the context of tobacco smoke and the 4000 or so chemicals produced, 60 of which are known carcinogens.

Recent research has shown that nicotine does have profound effects on the body. It raises the blood pressure and heart rate and interferes with normal processes in the nervous system.

We actually know relatively little about the complex interaction between nicotine and the nervous system. There is a large amount of ongoing research into the subject, with information coming to light almost every week.

Nicotine is unique in the way that it affects the body and brain. It developed in evolution as a powerful neurotoxin in certain plants to prevent them from being eaten by animals. In fact it has been widely used as an insecticide in agriculture.

'Neurotoxicity' simply means that a substance causes changes to the nervous system of the animal it is exposed to.

In order to understand why nicotine is so addictive, we need to know a little about how the nervous system operates:

The human nervous system basics

Fundamentally, the nervous system operates by turning on and off the billions of connections between nerve endings and allowing signals to either transmit, or not to transmit, kind of like a super-complex computer.

These different connections are responsible for everything that takes place in the body, whether it is mood, tiredness, action, digestion, or any other bodily function.

The connections are formed by neurotransmitters which 'plug' specific receptors in the nerve endings.



You will have heard of many of these neurotransmitters - adrenaline, seratonin, dopamine for instance - and they all change the configuration of the nervous system according to the volume that is let into the bloodstream.

Another of these neurotransmitters is called acetylcholine. Acetylcholine is responsible for a huge variety of functions - it triggers the action of muscles and also controls the release of other neurotransmitters. (Botox, which is used in cosmetic surgery to eradicate wrinkles, works because the main ingredient botulin prevents the release of acetlycholine where it is injected, thus paralyzing the muscles that cause the wrinkles).

In the brain, acetylcholine is responsible for activating the centers that deal with reward and arousal.

There are two types of receptor that acetylcholine can trigger - the muscarinic and the nicotinic acetylcholine receptors.

The nicotinic receptor is so named because in addition to acetylcholine, it will also be triggered by nicotine.

Nicotinic receptors and their effects

When the receptors are activated by nicotine, several changes take place:

• The neurotransmitter adrenaline (AKA epinephrine)is released into the body.
  

Adrenaline is a stimulating hormone and causes a rise in heart rate, respiration and blood pressure. It also causes the glucose levels in the blood to rise as it is released from the body's stores.

Adrenaline also causes the "fight or flight" response, making the user alert and in a state of readiness for action.

• The neurotransmitter dopamine is released in the reward parts of the brain, causing feelings of pleasure, satisfaction and reward.
  

As mentioned above, acetylcholine is a major controlling factor of arousal and reward, and it is by mimicking this that nicotine is believed to have its addictive nature.

A whole host of other neurotransmitters and hormones are also released as a direct and indirect result of the action of nicotine on the nervous system.

Uniquely, nicotine's effects are dose-dependent. Lower doses cause a stimulation effect, as dopamine and adrenaline are released into the brain - much like the action of psychostimulants such as cocaine and amphetamines.

At higher doses, nicotine causes relaxation, anti-anxiety and pain-relieving effects as seratonin and opioids are released into the brain.

It has been shown that smokers will take shorter puffs when they wish to get a stimulating effect and longer ones when they wish to relax.

When a smoker inhales cigarette smoke, nicotine enters the bloodstream almost instantly and within 7-10 seconds reaches the brain.

No other method of delivery gets nicotine into the system as fast. Nicotine replacement therapy (NRT) such as patches, gum and even the inhalator takes several minutes before the peak amounts are found in the bloodstream.

It is now belived that one of the key reasons that people become so dependent on nicotine is because of this rapid delivery. Most smokers will have experienced the nicotine 'hit' that occurs when smoking after a period without.

NRT works by breaking the reliance on this nicotine hit, while allowing the body to gradually become used to less and less nicotine over time.

However, since NRT does not provide the same feelings of instant pleasure as smoke, it has quite a high rate of failure as smokers find themselves in situations where only the instantaneous fix of a cigarette will do.

Freebase nicotine - Crack tobacco

Most of the nicotine in cigarette smoke is deposited as tiny 'lumps' of billions of particles of nicotine compounds stuck together and carried by cigarette smoke.

However, a proportion of the nicotine in a cigarette is not stuck to other particles, and enters the lungs as a gas when evaporated in the heat of the ember.

This 'freebase' nicotine is absorbed even more rapidly than nicotine in its solid form, and is believed to make the tobacco in which it is found even more addictive.

A freebase chemical is one that is stripped of part of its chemical makeup, allowing it to form a gas when heated. Crack cocaine is the most addictive form of that drug because it is the freebase version. It is delivered to the brain extremely rapidly and is thus far more addictive than in its regular form.

Studies have shown that different brands of tobacco contain different quantities of freebase nicotine. It is believed that this is due to the different strains of tobacco used, but the tobacco companies did spend years of research into artificially raising the quantity of freebase nicotine in their tobacco.

Ammonia is often used as an additive in tobacco manufacture and has the effect of increasing the amount of freebase nicotine in cigarette smoke.

The amount of freebase nicotine found in cigarette smoke varies amazingly depending on the brand. One study of 11 major brands found that freebase nicotine accounted for between 1.6% to 36% of the total volume.

The highest, 36%, was found in the organic brand American Spirit, while Marlboro was found to contain 9.6% freebase nicotine.

Additionally, a study by the Massachusetts Department of Public Health showed that in the period between 1998 and 2005 smokers were inhaling 11% more nicotine overall.

This is due to both an increase in the quantity of nicotine in tobacco, and because tobacco has been changed to burn more slowly, allowing the user more puffs per cigarette.

Since smoking was first revealed as the major killer that it is known to be today, the emphasis from governments and healthcare professionals has been on getting people to quit and break their nicotine dependence.

Smokers have effectively been given the choice "quit or die", but despite the anti-smoking campaigns many still continue to smoke because they have found themselves unable to break the addiction. In fact, only 3-7% of the general population are fully successful in quitting.

More recently, a different approach has been suggested by researchers. For those who cannot quit, why not give them a form of nicotine that satisfies the addiction, but does not contain the thousands of chemicals that cigarette smoke contains?

Swedish Snus and harm-reduction

This 'third way' was largely prompted by research in to smoking habits in Sweden, where it was found that a significant proportion of male nicotine users were using a form of oral-tobacco call "Snus".

Researchers discovered that compared to Swedish women, who do not culturally use Snus, the incidence of tobacco related death in men was far lower.

In other words, those who were using Snus were still addicted to nicotine, but were not dying.

Unfortunately, Snus is not well known outside of Sweden, and other forms of chewing tobacco such as those widely used in the United States are implicated in a wide variety of diseases due to chemicals that form during the curing process.

In Europe bans now exist to prevent new forms of tobacco from reaching the market. While this policy has the positive effect of limiting the tobacco industry, it also means that Snus can only be purchased in Sweden, since it has been on the market there for many years.

New technology - the e-cigarette

Another, newer form of nicotine delivery is the e-cigarette.

This hi-tech device delivers the nicotine to the user in a harmless cloud of water-vapor and flavorings and is becoming increasingly popular.

Unfortunately, it too exists in a legal gray area. Most countries only allow nicotine products to be sold under a medical license, which the e-cigarette does not yet have. The medical license is only given to products which can be shown to help users break their nicotine addiction - something that the e-cigarette is unlikely to be very good at since it delivers nicotine to the user in exactly the same way as a cigarette does.

However, the internet has enabled many people to get hold of the e-cigarette, and hopefully consumer pressure will force the legislators to reconsider the possibilities.

I have set up the website www.cigatron.com to try to get as many e-cigarette users as possible to get ready for the big fight that is going to occur when the crackdown begins.

New technology - Next Safety

Another device that has potential is the Next Safety device.

This is similar to the e-cigarette in that it is designed to deliver the nicotine to the user through the lungs, allowing them to get the 'hit' that is delivered by cigarettes.

This is still in its prototype stage, and will face the same legal pressures as the e-cigarette, although it is being made by a medical device company, so it may have an easier route to market.

Since the dangers of smoking were first made publicly known in the 1950s, most of the research carried out has concentrated on the carcinogens and other chemicals such as carbon monoxide that are found in tobacco smoke.

Given nicotine's central role in tobacco usage, it has been remarkably under-researched, mainly because it was quickly realized that, compared to the other chemicals found in smoke, its effects are minimal.

However, several recent studies suggset that nicotine has the ability to cause some profound changes in the brain, disrupting normal brain processes and interfering with emotions and decision making. It has also been found to play a key role in cancer as it speeds up the growth of tumours.

Teen brains altered by nicotine

A study by scientists at the Yale University School of Medicine showed that teenagers who smoke develop changes to the white matter that carries signals to and from the ear.

The study showed that the brain is particularly susceptible to nicotine in adolescence because the neural pathways are still fine tuning on the way to maturity.

Another, earlier study showed that teenage smokers suffer from disturbances to their visual and auditory attention compared to their non-smoking peers and that boys are especially vulnerable.

The changes mean that smokers are less able to hear what is said, so if a teen is already struggling at school, then this disruption could tip them towards failure.

Similar changes were also detected in the brains of children whose mothers smoked during their pregnancy.

It is not yet known whether the damage is reversible when the smoker quits nicotine.

Smokers' judgement clouded by nicotine

A group of smokers and non-smokers were asked to take part in a simulation stock-trading game. Their performance was analysed each 'round' and they were given feedback on their investment returns.

The smokers in the group were found to perform worse than the non-smokers. They were able to process the information between rounds, but not able to allow it to inform their future decision making as they went on to invest in almost the same manner as before.

It is not yet known whether this is because of changes in the brain caused by nicotine, or whether people who are more prone to addiction already have this brain structure.

Tumor growth sped up by nicotine

Many smokers on discovering that they have developed cancer take an 'it's too late now' approach to their habit, but research now shows that in fact they could be making themselves far less likely to survive.

Altough nicotine itself is not a cancer-causing chemical, it has an accelerating effect on the growth of tumors.

Additionally, it has been found that people in intensive care suffer a greater risk of death if they are using NRT products than those without. This is believed to be due to nicotine causing narrowing of the blood vessels and raising blood pressure.

It stands to reason, therefore, that anyone undergoing hospital treatment should seriously attempt to get nicotine out of their system before they go in.

As explained above, nicotine stimulates the nicotinic cholinergic receptors in the body. A nicotine overdose is characterized by the symptoms caused by an excessive stimulation of these receptors.

If you suspect an overdose, call the emergency services.

Although the lethal dose for an adult is in the region of 40-60mg, symptoms can show after ingesting only 4-5 mg, the amount found in 5 high-strength cigarettes. Inexperienced smokers can suffer some of these symptoms by chain-smoking.

For children the lethal dose is far lower, and even small doses are extremely dangerous.

Syptoms

Symptoms of nicotine overdose include:

• Vomiting and nausea, diarrhea
  
• Headaches
  
• Difficulty breathing
  
• Pallor
  
• Perspiration (sweating)
  
• Throat burn
  
• Palpitations
  
• Hearing and visual disturbances
  
• Stomach pains/cramps
  
• Seizures
  
• Weakness
  
• Salivation and drooling
  
• Unconsciousness
  
• Death
  

Treatment

The treatment for nicotine overdose centers on getting it out of the system and preventing any more from being absorbed.

Firstly the patient is stabilized to ensure that their heart is pumping and is still breathing.

Vomiting is then induced artificially (although the sufferer will probably already be vomiting due to the overdose), or the stomach is pumped to clear it.

Activated charcoal is then introduced to the stomach where it is left to absorb any more nicotine that may not have been cleared.