How Quitting Smoking Can Impact the Medicines You Take

Prescription drugs are known to interact with other drugs and certain foods, but they can also be affected by smoking—and smoking cessation.

Foods that we eat are broken down (metabolized) into nutrients that our bodies can use. This process starts with enzymes, which act as catalysts for the digestive process. There are many types of enzymes. Some of them help break down proteins, some work on carbohydrates, and others on fats.

In a similar way, there are enzymes that metabolize prescription drugs. One of these enzymes, CYP1A2, is affected by some of the chemicals in cigarette smoke. These toxins, called PAHs (polycyclic aromatic hydrocarbons) are known to be some of the most potent carcinogens in tobacco smoke.  

When PAHs come in contact with CYP1A2 the enzyme becomes more active. This causes medicines that are broken down by CYP1A2 to be metabolized more quickly than they should be. As a result, smokers often require a higher dose than would normally be given.

When smoking stops abruptly, such as going into the hospital where smoking isn't allowed or quitting cold turkey, CYP1A2 activity slows down and the larger dose can suddenly be too much.  The chance of negative side effects of medications abruptly increases as well.

It is important that medications be reviewed and possibly adjusted by the prescribing doctor when a person quits smoking.

As you can see from this list, a wide variety of medications are metabolized by CYP1A2. Some of them won't cause an adverse reaction following smoking cessation, but others can cause serious side effects if the dose isn't modified or adjusted once a person stops smoking. Don't hesitate to share your quit smoking journey with your healthcare team so that they can keep an eye on any changes you might be experiencing.

• Alosetron (Lotronex): antidiarrheal used to treat irritable bowel syndrome
• Clozapine: sedative drug used to treat schizophrenia
• Flutamide (Eulexin): hormone-based chemotherapy medicine
• Fluvoxamine (Luvox): used to treat obsessive or compulsive behaviors 
• Frovatriptan (Frova): used to treat migraine headaches
• Haloperidol (Haldol): treats schizophrenia, acute psychosis, and is used for tics and vocal utterances of Tourette's syndrome
• Imipramine (Tofranil): used to treat depression
• Melatonin: over the counter supplement used for sleep
• Mexiletine (Mexitil): antiarrhythmic used to treat irregular heartbeat
• Mirtazapine (Remeron): antidepressant used to treat depression. 
• Olanzapine (Zyprexa): used for schizophrenia, bipolar disorder
• Propanolol (Inderal): used to treat tremors, angina (chest pain), high blood pressure, heart rhythm disorders, and other heart or circulatory conditions. Also used to treat migraine headaches
• Ramelteon (Rozerem): sedative used for insomnia
• Rasagiline (Azilect): MAOI and antidepressant that can be used to treat Parkinson's disease

Most ex-smokers will tell you that coffee had a much stronger effect on them after quitting smoking. The usual cup or two in the morning left them jittery and nervous. They'd chalk it up to the lack of nicotine, and that does play a role, but it probably had more to do with CYP1A2.

Smokers metabolize caffeine at approximately four times the rate of non-smokers. It is no wonder that drinking the usual amount of coffee or other caffeinated drink is suddenly uncomfortable following smoking cessation. If you recently quit, you might try cutting your caffeine consumption by half and see how you feel. You can then reduce or increase based on that.

Nicotine in tobacco and in nicotine replacement therapy can also influence how the body is able to respond to some medications.

Nicotine constricts blood vessels and may inhibit the absorption of insulin shots.

Nicotine is a stimulant that raises heart rate and blood pressure.  It may contribute to reduced sensitivity to medications used to treat the same.  It is also associated with reduced sedation from benzodiazepines (tranquilizers) and less pain relief from some opioids.

If you take any prescription medicines and have stopped smoking (or you plan to), check in with your doctor to review how they may be affected by smoking cessation.

The good news is that quitting smoking will improve your health and vitality. You may even find that some medications can be eliminated once your body recovers from nicotine addiction.

If you're ready to quit, use these quit smoking resources as a starting point. There is no time like the present to start work on making your dreams a reality.