Nicotine use artificially increases dopamine production in the body so when you quit smoking, many of the withdrawal symptoms are caused by an attempt to find a new healthy level of dopamine production.
Here is an article I found at livestrong.com which could help you naturally regulate dopamine production during smoking cessation:
How Do I Increase Dopamine Production?
Dopamine is neurotransmitter found in the brain and essential for the normal functioning of the central nervous system. Dopamine is derived from the amino acid tyrosine and is the precursor to norepinephrine and epinephrine. Among its effects, dopamine enhances the pleasure pathway, as well as memory and motor control. Drugs, such as cocaine and nicotine, increase dopamine, and this is why they are often so addictive. Dopamine production can be increased through healthy lifestyle modifications.
Exercise most days of the week. Cardiovascular exercise has been shown to increase dopamine levels. A study by Giselle M. Petzinger and other researchers, in the "Journal of Neuroscience" of May 16, 2007, showed that mice running on a treadmill for up to 60 minutes per day for five days per week showed increases in dopamine production and uptake.
Reduce stress through relaxation and other meditative activities such as yoga. Stress reduces dopamine levels and often leads to depression. Practice deep breathing techniques and take time each day to do something calming. Deep breathing is done by inhaling deeply through your nose, filling your chest cavity fully, then exhaling very slowly through your mouth.
Take antioxidants, such as vitamin C, B6 and E. According to "Integrative Psychiatry", dopamine is easily oxidized, and these antioxidants will fight off the oxidation that lowers your dopamine levels.
Reduce the amounts of foods you ingest that are processed and high in fat, cholesterol and sugars. Replace these foods with fresh fruits and vegetables that are rich in antioxidants, such as berries, spinach and broccoli.
Eat foods that are high in an amino acid called tyrosine. Bananas, fish, almonds and watermelons are examples of foods that help to produce tyrosine, which is then converted into dopamine and norepinephrine, resulting in increased dopamine levels.
Talk to your doctor about whether taking a dopamine precursor might be beneficial. A precursor is a chemical that is transformed into another compound. Dopamine is derived from the amino acid, or precursor, phenylalanine. This chemical is found in foods such as meats, milk and oats.