My question is simple. Is it possible to be immune to the effects of nicotine addiction? I am a regular smoker. Have been for around 4 years. I've found that I can quit for months without feeling the need for a cig although I still get the head rush it provides. I admit I have a habit but physically I do not feel withdrawals when I quit. Is there a reason for this?

I still get the head rush it provides...I admit I have a habit
It doesn't sound like you are immune to nicotine.

DrBill will probably weigh in with some thoughts on addiction.

Immunity to nicotine probably skirts the problem of addiction.

Nicotine is only mildly reinforcing. Cigarette smoking however is a complex and pervasive addiction.

Chemically, cigarette smoke contains thousands of compounds, most undefined. Most have been added since the mid-1970s purportedly to enhance the taste and enjoyment of cigarette smoking. In other words, to make it a more rewarding experience thereby reinforcing the desire to smoke.

There are people that smoke only infrequently, never develop a need or compulsion to smoke. We call them chippers. This same phenomenon exists even among cocaine users and other potent (highly reinforcing) drugs. Remain infrequent recreational users and never advance to addiction.

Doubt that your experience represents an immunity to nicotine as it plays only a small (albeit important) part in cigarette smoking.

The fact that you don't experience withdrawal isn't at all unusual. Withdrawal varies widely from one individual to another, mild to life threatening, even among chronic drug users. With smoking it is the long-lasting nature of the desire to smoke rather than intensity at cessation that is compelling.