[NinjaViking]

Because cigarettes deliver nicotine very, very fast, giving an instant and pleasant rush. After an hour or so the nicotine level in your blood has fallen quite a lot and you'll be craving another one.

E-cig nicotine delivery happens slower and you avoid both the highs and the crashing lows. That makes it a lot easier to cut down to insignificant amounts of nicotine over a few months.

[jdietrich]

Tobacco smoke also contains monoamine oxidase inhibiting compounds, which are believed to drastically increase the addictive potential of nicotine. Rats are largely indifferent to nicotine alone, but will compulsively self-administer nicotine in combination with an MAOI.

http://www.sciencedirect.com/science/article/pii/S0024320506... http://jneurosci.org/content/25/38/8593.long http://www.sciencedirect.com/science/article/pii/S0091305703...

Cigarettes do give a more immediate and intense nicotine 'hit'. Ammonia compounds are added to cigarette tobacco, which increase the proportion of freebase nicotine to nicotine salts. Cigarettes are, in a very literal sense, the crack cocaine of nicotine delivery.

http://www.ash.org.uk/files/documents/ASH_623.pdf

[facetube]

In a lot of drugs, euphoria is at least partially proportional to the rate of blood level increase, e.g. [1].

[1] http://www.dddmag.com/article/2009/07/question-opioid-euphor...