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Our 2nd article on Smoking to help you "Stay stopped" - Interesting information highlighting adverse interaction between tobacco smoke and medications

Posted by Eamonn Brady on

Smoking Cessation Part 2


Drug interactions with smoking

Drug interactions between tobacco smoke and drugs are often underestimated by patients and clinicians alike. Tobacco smoke affects the absorption, distribution, metabolism (or elimination) of drugs thus potentially giving an altered response. Tobacco smoke accelerates the metabolism of certain drugs by inducing hepatic cytochrome P450 enzymes (primarily CYP1A2). It is believed the polycyclic aromatic hydrocarbons in tobacco smoke are responsible for the induction of cytochrome P450 rather than nicotine meaning that nicotine replacement products do not have the same degree of drug interactions


The HSE’s Brief Intervention for Smoking Cessation programme (Table 1) documents the main tobacco drug interactions with caffeine and fluvoxamine being considered the most clinically significant interactions.


Table 1:


  Possible Effects when giving up smoking versus when smoking


(used for anxiety)

• Decreased sedation and drowsiness.


(used for fast heart rate, high blood pressure, heart failure and less often for anxiety and migraine)  

• Less effective antihypertensive (blood pressure control) and heart rate control.



• Clearance increased by 56% so may be over 50% less effective.


(Anti-psychotic drugs used for mood disorders)

• • Smokers may experience less sedation and hypotension (lower blood pressure) and require higher dosages than nonsmokers.


(Anti-psychotic drugs used for mood disorders)

• Blood concentrations decreased by 28%.


(used for irregular heart rate, especially fast heart rate)

• Clearance increased by 61%; blood levels decreased by 25%.

• Smokers may require higher dosages.



• Clearance increased by 25%; decreased blood concentrations (47%).

• Dosage modifications not routinely recommended but smokers may require higher dosages.


(Anti-psychotic drugs used for mood disorders)

• Clearance increased by 44%; blood concentrations decreased by 70%.


(Blood thinner)

• Mechanism unknown but increased clearance and decreased half-life observed.

• Smokers may require higher dosages.


(used for diabetics)

• Insulin absorption may be decreased due to peripheral vasoconstriction (narrowing of blood vessels); smoking may cause release of endogenous substances that antagonise the effects of insulin. Smokers may require higher dosages.


(Anti-psychotic drugs used for mood disorders)

• Clearance increased by 40-98%. Dosage modifications not routinely recommended but smokers may require higher dosages.

Opioids (propoxyphene, pentazocine)- used for severe pain

• Decreased analgesic effect; higher dosages necessary in smokers.

• Mechanism unknown.


(older beta blocker; uses described above)

• Clearance (via side chain oxidation and glucuronidation) increased by 77%.

Oral contraceptives

• Increased risk of cardiovascular adverse effects (e.g., stroke, myocardial infarction, thromboembolism) in women who smoke and use oral contraceptives.

• Risk increases with age and with heavy smoking (15 or more cigarettes per day) and is quite marked in women over age 35 years.


(used for asthma and COPD)

• Clearance increased by 58-100%; half-life decreased by 63%.

• Theophylline levels should be monitored if smoking is initiated, discontinued, or changed.

• Maintenance doses are considerably higher in smokers.

Table 1 Reference: Significant tobacco/ drug interactions (Reference: Brief Intervention for Smoking Cessation (HSE) 2012


Many of the tobacco/ drug interactions involve drugs used for mental health disorders. It is well documented that people with mental health disorders have a higher propensity to smoke so drug interactions can be more of an issue for these patients and need to be considered when patients are giving up smoking as the concentration of the drug in the blood stream may be increased. However, many of the drugs which tend to have the more significant interactions are used less frequently nowadays


What is BPro Cardio Screen Service?

BPro Cardio Screen measures artery stiffness to identify risk of blockages and cardiovascular and circulatory disease. BPRo is placed like a watch on your wrist and is pain free. A pulse wave reads and calculates a wave signal that indicates the elasticity of large, small, and peripheral artery walls as well as tests for stress, central blood pressure, heart rate, and more. It is now €35 (was €50); it only takes about 15 minutes. The next clinic is Saturday February 26th (from 9am to 5pm) at Whelehans Pearse St. Book online on the Whelehans Website or by calling Whelehans at 04493 34591.


To be continued…next week

For comprehensive and free health advice and information call in to Whelehans, log on to or dial 04493 34591 (Pearse St) or 04493 10266 (Clonmore). Email queries to Find us on Facebook.


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