NicVAX is a relapse prevention therapy designed to stimulate the immune system to produce antibodies that bind to nicotine in the bloodstream and prevent and/or slow it from crossing the blood–brain barrier and entering the brain. With a reduced amount of nicotine reaching the brain, neurotransmitter release is greatly lessened and the pleasurable, positive-reinforcing effects of nicotine are diminished. Pre-clinical studies with the vaccine have shown that vaccination slows and decreases the amount of nicotine that reaches the brain and blocks the effects of nicotine, including effects that can reinforce and maintain addiction in animals. Therefore, if a recently quit tobacco smoker is vaccinated and has a tobacco cigarette after the immunization series is completed, the antibodies generated by the vaccine bind nicotine and alter its distribution into the brain. Because not enough nicotine enters the brain, addiction-relevant neural pathways are not activated. No pleasure is derived from the tobacco cigarette and the vaccinated subject does not relapse and begin smoking again.