Cigarette smoke  and nicotine induce hepatic enzymes.  
Smoking Cessation
Cessation of smoking may alter the response to concomitant administration of various drugs in patients who previously smoked.   
Potential pharmacokinetic interaction (decreased metabolism and increased blood concentrations of certain drugs) with cessation of smoking.  
Consider the effect of smoking cessation in patients receiving nicotine replacement therapy when patient is receiving other drugs concomitantly.       
Sympathomimetic and Sympatholytic Drugs
Potential pharmacodynamic interaction (increased circulating plasma concentrations of cortisol and catecholamines); may require dosage adjustment of sympathomimetic (adrenergic) or sympatholytic (adrenergic blocking) drugs.
Possible altered absorption of transdermal nicotine from drugs producing cutaneous vasoconstriction (e.g., sympathomimetic agents) or vasodilation (e.g., antihypertensive agents).
Foods Affecting Salivary Acidity
Transient decrease of salivary pH may inhibit buccal absorption of nicotine from gum, lozenge, or oral inhaler. 
Specific Drugs and Foods
Drug or Food
Interaction
Comments
Acetaminophen
Smoking cessation may decrease metabolism and increase blood concentrations of acetaminophen
Decrease dosage of acetaminophen as required
Acidic beverages (e.g., coffee, juices, carbonated soft drinks)
May inhibit buccal absorption of nicotine from gum, lozenge, or orally inhaled drug  
Do not eat or drink for 15 minutes before and during gum or lozenge therapy   
Adrenergic agonists (e.g., isoproterenol, phenylephrine)
Smoking cessation may decrease circulating plasma concentrations of catecholamines
Increase dosage of adrenergic agonists as required
Adrenergic antagonists (e.g., prazosin, labetalol)
Smoking cessation may decrease circulating plasma concentrations of catecholamines
Decrease dosage of adrenergic antagonists as required
β-Adrenergic blocking agents (e.g., propranolol)
Smoking cessation may decrease metabolism and increase blood concentrations of β-adrenergic blocking agents     
Smoking cessation may restore the decreased cardiac output and hypotensive effect induced by propranolol  
Decrease dosage of β-adrenergic blocking agent as required
Bupropion
Possible increased risk of hypertension
May be used concomitantly with transdermal nicotine therapy
Caffeine
Smoking cessation may decrease metabolism and increase blood concentrations of caffeine     
Decrease dosage of caffeine as required
Furosemide
Smoking cessation may increase diuretic effects of furosemide  
Glutethimide
Smoking cessation may decrease absorption of glutethimide 
Insulin
Smoking cessation increases absorption of subcutaneous insulin
Monitor blood glucose closely; adjust insulin dosage as needed
Nasal vasoconstrictors (e.g., xylometazoline)
Delays time to peak plasma concentration of nicotine nasal spray
Oxazepam
Smoking cessation may decrease metabolism and increase blood concentrations of oxazepam     
Decrease dosage of oxazepam as required     
Pentazocine
Smoking cessation may decrease metabolism and increase blood concentrations of pentazocine     
Decrease dosage of pentazocine as required     
Propoxyphene
Smoking cessation may decrease metabolism of propoxyphene 
Decrease dosage of propoxyphene as required 
Theophylline
Smoking cessation may decrease metabolism and increase blood concentrations of theophylline     
Monitor plasma concentrations and adjust dosage of theophylline as required
Tricyclic antidepressants (e.g., imipramine)
Smoking cessation may decrease metabolism and increase blood concentrations of tricyclic antidepressants     
Adjust dosage of tricyclic antidepressant as required 
 Nicotine drug interactions (more detail)
