In many people, nicotine from cigarettes stimulates receptors in the brain to release dopamine, triggering a pleasure response. Over time, the number of nicotine receptors increases and changes your brain's anatomy. When you quit smoking, you cut off the brain's pleasure response because the receptors don't get nicotine, triggering nicotine withdrawal symptoms. If you stick it out and use stop-smoking products to help with withdrawal symptoms and cravings, the number of nicotine receptors returns to normal, helping you quit smoking for good.