There's a reason your GP might bring up prescription medication when you tell them you want to quit. It's not because quitting with willpower alone is impossible -- people do it -- but because the data on certain medications is hard to ignore. For some people, pharmacotherapy changes the odds significantly.
Two medications dominate the evidence: varenicline (sold as Champix in the UK and Europe, Chantix in the US) and bupropion (Zyban in the UK, also sold as Wellbutrin for depression). Here's what each does, what the research shows, and what a conversation with your doctor about them might look like.
Varenicline (Champix): How It Works
Varenicline works through a dual mechanism that targets the core problem of nicotine dependence directly.
Nicotine binds to a specific receptor subtype in the brain (alpha-4 beta-2 nicotinic acetylcholine receptors) and triggers dopamine release -- the reward signal. Varenicline is a partial agonist at those same receptors. That means two things:
First, it activates the receptor at a lower level than nicotine does, providing enough stimulation to reduce withdrawal symptoms without the full "hit" of a cigarette.
Second, because it's occupying the receptor, nicotine from a cigarette has far less effect if you do smoke. The reward is blunted. Many people on varenicline report that cigarettes smoked during the medication course tasted different or less satisfying -- that's the mechanism working.
The standard course is 12 weeks, starting the medication 1--2 weeks before your quit date to build up therapeutic levels. Some people benefit from an extended 24-week course.
What the Evidence Shows
A 2016 Cochrane review including 27 trials found that varenicline approximately tripled continuous abstinence rates at 6 months compared to placebo. When compared directly to NRT, it consistently shows higher quit rates. When compared to bupropion, it also outperforms it.
Cochrane reviews comparing cessation pharmacotherapies have consistently confirmed varenicline's position as the most effective single agent available.
The Neuropsychiatric Warning: What Happened
From 2009 to 2016, varenicline carried a black box warning (the FDA's strongest warning) about potential neuropsychiatric side effects: depression, suicidal ideation, changes in behavior. This was a significant deterrent to prescribing.
In 2016, results from the EAGLES trial -- a large, rigorous study involving 8,000+ participants -- showed that neuropsychiatric events were not significantly elevated in varenicline users compared to nicotine patch users. The FDA removed the black box warning.
The current evidence suggests the neuropsychiatric risk was substantially overstated. People with pre-existing psychiatric conditions should still discuss this with their doctor, but the warning should not automatically rule out varenicline for most people.
Common Side Effects
The most common side effect is nausea, affecting up to 30% of users. It's usually manageable when the medication is taken with food and a full glass of water. For most people, nausea reduces over the first 1--2 weeks as the body adjusts.
Other reported effects: vivid or unusual dreams, headaches, insomnia. These typically diminish over the course of treatment.
Bupropion (Zyban): How It Works
Bupropion was originally developed as an antidepressant (it's still prescribed as Wellbutrin for depression). Its effectiveness for smoking cessation was discovered when patients taking it for depression incidentally stopped smoking at unusually high rates.
Its exact mechanism for smoking cessation isn't fully understood. It inhibits the reuptake of dopamine and norepinephrine in the brain, which appears to reduce nicotine cravings and withdrawal symptoms. It may also partially block nicotinic receptors, similar to varenicline but less specifically.
The standard course is 7--12 weeks, starting 1--2 weeks before the quit date to reach therapeutic levels.
What the Evidence Shows
A 2014 Cochrane review found that bupropion approximately doubles quit rates compared to placebo. It's less effective than varenicline in head-to-head trials, but still significantly more effective than placebo or unassisted quitting.
One advantage: bupropion can be particularly useful for people who are also managing depression alongside quitting -- two goals addressed by one medication. This should always be managed in consultation with a doctor.
Contraindications
Bupropion is not suitable for everyone. It's contraindicated in people with a history of seizures, eating disorders (particularly bulimia or anorexia), or who are taking monoamine oxidase inhibitors (MAOIs). These are screening questions your GP will ask.
Common Side Effects
Dry mouth and insomnia are the most commonly reported. Insomnia is often managed by taking the dose in the morning rather than at night. Some people also experience headaches and dizziness in the first week.
Combining Medications
Research has explored whether combining medications improves outcomes.
Varenicline + NRT: Some studies suggest that adding a nicotine patch to varenicline may provide modest additional benefit compared to varenicline alone. This approach is used off-label by some clinicians.
Bupropion + NRT: The evidence for this combination is mixed. It may provide some benefit over either alone, but the improvement is less consistent than the varenicline + NRT data.
The most important combination isn't medication with medication -- it's medication with behavioral support. Every major Cochrane review on cessation pharmacotherapy shows better outcomes when medication is combined with counseling or structured behavioral support than medication alone.
Getting a Prescription
In the UK, both varenicline and bupropion are available on NHS prescription. Your GP is the starting point. Stop Smoking services (accessible through your GP or directly) can also prescribe these medications alongside structured behavioral support.
Before prescribing, your GP will ask about: other medications you're taking, psychiatric history, seizure history, cardiovascular conditions, and pregnancy status.
If you're uncertain whether either medication is appropriate for you, that conversation belongs with your GP -- not a blog article. The right answer depends on your specific situation, current medications, and health history.
How Behavioral Support Changes the Equation
Medications reduce the physiological pull toward nicotine. They don't remove the cue-response patterns -- the automatic reach for a cigarette after a meal, during a call, when you're stressed.
The most effective quit plans address both. A medication managing withdrawal buys you space. Behavioral tools help you use that space to build different patterns.
Milo works alongside whatever cessation method you choose, including medication. Your Fagerstrom score from onboarding tells us how much of your smoking is physiological dependence vs behavioral habit -- and the support adapts accordingly.