I have never used this stuff before but a heroin addict offered some to me before and I said "Fuck no!". I asked him to try it for me and usually he will try drugs for me but hes a heroin addict and not even he would touch the stuff. I wanted to use it but damn hows it so addictive. I know like one person whose done it but hes able to resist addiction to anything I swear he doesn't even get withdrawals from any drug. How is it that a psychological addiction can be so strong that it can be stronger on the mind than physical addictions?
Methamphetamine is addictive due to the fact that it reuptakes dopamine (a neurotransmitter) in the brain. Dopamine is resposnible for the pleasure feelings people have when they are having sex, eating their favorite food, maybe doing their favorite activity, and it's the overall joy that someone has. Methamphetamine (and most drugs that are addictive) release a lot dopamine (that the body is not meant to release that much) and you have a feeling of euphoria, confidence, well being, and it's a feeling that is almost impossible to describe in words. Therefore, addicts have a hard time enjoy life without the drug due to the fact that their brain does not release dopamine at the level that it wants it to when you injest methamphetamine.
Adding to (and perhaps restating some of) what whocaresdude91 said above:
Methamphetamine is a powerful central nervous stimulant; it produces mental effects similar to other stimulants (such as amphetamines, cocaine) but at smaller doses and far fewer peripheral side effects. In other words, it acts much more on the brain (better mood, focus, sociability, etc) than the body (increased blood pressure, heart rate, etc).
Methamphetamine is basically amphetamine with the methyl group added to it. This methyl group makes it more fat soluble so it crosses the blood-brain barrier much quicker and easier than most other stimulants, and also causes it to be more resistant to MAO degradation.
Unlike other stimulants such as cocaine, methamphetamine (and amphetamines at high doses) also effect(s) serotonin levels, which accounts for its more potent mood-enhancing effects. Also unlike other stimulants, in addition to indirectly inhibiting monoamine reuptake, it also reverses the flow of them, resulting in more dopamine, serotonin and norepinephrine in the synapse. (It basically goes in the cell and pumps them out.)
It is also very neurotoxic. One reason why this may be is because methamphetamine causes very high levels of dopamine. When dopamine is eventually broken down by MAOs, it produces chemically-reactive molecules containing oxygen (free radicals). This results in oxidative stress, potentially damaging neurons ("killing brain cells").
The huge increase in dopamine may also play into why it is so addictive. Dopamine is the brain's primary reward chemical. The first few times someone does meth, after they "crash", the reason they feel so bad is because the levels of the neurotransmitters are so low. Usually, this feeling goes away after a couple night's good sleep (depending on how much was done) after the brain replenishes its supply. Chronic or extremely high doses of meth, however, can cause the brain receptors to downregulate to compensate for all the dopamine. This means more dopamine is required to to achieve the same effect; that is, even if the brain were to replenish its supply, it still wouldn't help so much since more dopamine would be required to function normally, amounts the brain doesn't naturally do.
This last paragraph may be the most relevant to answering the question of "Is Meth really that addictive?". While in the short term, it may seem that it's possible to control, it can quickly lead to a downward spiral without even realizing it until it's too late.
(I know I jumped back and forth between referring to the three different neurotransmitters and just dopamine, but dopamine is the most important of the three.)
I also apologize for any typos or grammatical errors I made. I am in sort of a rush and didn't have time to double check everything.
Mr. Hamster would like to clarify just one point about SWIArctangent's post.
Methamphetamine is metabolized, though demethylation in the liver into the active metabolite amphetamine. The MAO inhibition effects are actually caused by amphetamine competing for MAO since amphetamine is a monoamine and is broken down by MAO-A and MAO-B.
Also, he believes that "Unlike other stimulants... serotonin" was probably meant to be "Like other stimulants."
Other than that, SWIArctangent is right on the money.