Nicotine use can have many different effects on body functions, both positive and negative. Nicotine acts as both a stimulant and depressant on your body. The use of nicotine:

• Acts as an appetite suppressant (for this reason, the fear of weight gain affects some people's willingness to stop smoking).
• Boosts mood and may even relieve minor depression. Many people will feel a sense of well-being.
• Elevates the blood level of glucose (blood sugar) and increases insulin production.
• Increases bowel activity, saliva, and bronchial secretions.
• Increases heart rate by around 10 to 20 beats per minute.
• Increases blood pressure reading by 5 to 10 mmHg (because it constricts the blood vessels).
• May cause sweating, nausea, and diarrhea.
• Stimulates memory and alertness. People who use tobacco often depend on it to help them accomplish certain tasks and perform well.

Symtoms of nicotine withdrawal generally start within 2 - 3 hours after the last tobacco use, and will peak about 2 - 3 days later. Symptoms may be severe, depending on how long you smoked and how many cigarettes you smoked each day. Common symptoms include:

• An intense craving for nicotine
• Anxiety, tension, restlessness, frustration, or impatience
• Difficulty concentrating
• Drowsiness and trouble sleeping, as well as bad dreams and nightmares
• Headaches
• Increased appetite and weight gain
• Irritability or depression

A milder form of nicotine withdrawal that involves some or all of these symptoms can occur when a smoker switches from regular to low-nicotine cigarettes or significantly cuts down on the number of cigarettes smoked.

Symptoms of nicotine withdrawal can mimic, disguise, or aggravate the symptoms of other psychiatric problems, according to the American Psychiatric Association.