When you stop smoking, you may have nicotine withdrawal symptoms with or without using medication such as varenicline. This includes feeling restless, depressed, angry, frustrated, or irritated.
Stop taking varenicline and call your doctor if you have if you feel depressed, agitated, hostile, aggressive, or have thoughts about suicide or hurting yourself.
Do not drink large amounts alcohol. Varenicline can increase the effects of alcohol or change the way you react to it.
Before taking this medicine
You should not use varenicline if you used it in the past and had:
a serious allergic reaction--trouble breathing, swelling in your face (lips, tongue, throat) or neck; or
a serious skin reaction--blisters in your mouth, peeling skin rash.
Tell your doctor if you have ever had:
depression or mental illness;
a seizure;
kidney disease (or if you are on dialysis);
heart or blood vessel problems; or
if you drink alcohol.
Tell your doctor if you are pregnant. It is not known whether varenicline will harm an unborn baby if you use the medicine during pregnancy. However, smoking while you are pregnant can harm the unborn baby or cause birth defects.
If you breast-feed while using  varenicline, your baby may spit up or vomit more than normal, and may have a seizure.
Varenicline is not approved for use by anyone younger than 18 years old.
How should I take varenicline?
Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.
When you first start taking varenicline, you will take a low dose and then gradually increase it over the first several days of treatment. Take varenicline regularly to get the most benefit.
You may choose from 3 ways to use varenicline. Ask your doctor which method is best for you:
Set a date to quit smoking and start taking varenicline 1 week before that date. Make sure to quit smoking on your planned quit date. Take varenicline for a total of 12 weeks.
Start taking varenicline before you set a planned quit date, and choose a quit date that is between 8 and 35 days after you start treatment. Take varenicline for a total of 12 weeks.
Start taking varenicline and gradually reduce the number of cigarettes you smoke each day over a 12-week period, until you no longer smoke at all. Then take varenicline for another 12 weeks, for a total of 24 weeks.
Take varenicline after eating. Take the medicine with a full glass of water.
When you stop smoking, you may have nicotine withdrawal symptoms with or without using medication such as varenicline. Withdrawal symptoms include: increased appetite, weight gain, trouble sleeping, slower heart rate, feeling anxious or restless, and having the urge to smoke.
Smoking cessation may also cause new or worsening mental health problems, such as depression.
Stop taking varenicline and call your doctor if you have if you feel depressed, agitated, hostile, aggressive, or have thoughts about suicide or hurting yourself.
Store at room temperature away from moisture and heat.
What happens if I miss a dose?
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.
Get your prescription refilled before you run out of medicine completely.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
