Is it safe for a patient with anxiety and depression on mirtazapine to start varenicline for smoking cessation, or should they be referred to their GP?

You can safely prescribe varenicline to your patient with anxiety and depression on mirtazapine without referral to their GP.

The most robust evidence demonstrates that varenicline is both safe and effective in patients with psychiatric disorders, including depression and anxiety, and does not require specialist referral for initiation.

Key Evidence Supporting Safety

The landmark EAGLES trial (2016) provides the strongest evidence for this decision 1. This large double-blind RCT enrolled over 8,000 participants, including 4,074 individuals with diagnosed psychiatric disorders. Critically, rates of neuropsychiatric adverse events in individuals receiving varenicline were not significantly increased relative to those receiving nicotine patches or placebo in either the psychiatric or non-psychiatric cohorts 1.

Specific Findings in Depression/Anxiety Populations:

• A dedicated trial in 525 smokers with stably treated current or past major depression found varenicline increased smoking cessation rates without exacerbating depression or anxiety symptoms 2
• Varenicline achieved 35.9% abstinence vs 15.6% for placebo at weeks 9-12 (OR 3.35) in this depressed population 2
• No clinically relevant differences in suicidal ideation or behavior were observed 2
• A 2023 study confirmed varenicline was equally effective for smokers with and without depressive symptoms, while bupropion showed reduced effectiveness in those with depressive symptoms 3

Practical Management Approach

You Should Prescribe Varenicline If:

• Patient's depression/anxiety is stably treated (as yours appears to be on mirtazapine)
• No history of seizures or brain metastases
• Patient can tolerate monitoring for neuropsychiatric changes

Standard Dosing Protocol 1:

• Days 1-3: 0.5 mg once daily
• Days 4-7: 0.5 mg twice daily
• Weeks 2-12: 1 mg twice daily (if tolerated)
• Start 1-2 weeks before quit date

Monitoring Requirements 1, 4:

You must monitor for development or worsening of:

• Depression or suicidal ideation
• Agitation, hostility, or aggression
• Anxiety or panic symptoms

Instruct the patient to discontinue varenicline immediately and contact you if these symptoms occur 1, 4.

Follow-up within 2 weeks of starting pharmacotherapy is recommended 1.

Why No Specialist Referral is Needed

The guidelines explicitly state varenicline is a preferred primary therapy for smoking cessation 1. The European cardiovascular guidelines note that while a psychiatric history should be taken before prescription, they recommend varenicline can be prescribed with appropriate monitoring 5. Current morbidity or distress may suggest postponement of drugs other than NRT, but your patient appears stable on mirtazapine 5.

Drug Interaction Considerations:

There are no clinically meaningful pharmacokinetic drug interactions between varenicline and antidepressants 4. Preclinical studies specifically examined varenicline with serotonergic antidepressants and found no potentiation or attenuation of antidepressant effects 6. While mirtazapine is not a pure SSRI, the lack of interaction with serotonergic agents is reassuring.

Common Pitfalls to Avoid

1. Don't withhold varenicline based on outdated black box warnings - The FDA black box warning has been removed based on EAGLES trial data showing no increased neuropsychiatric risk 1

2. Don't assume all psychiatric patients need specialist referral - Only refer if depression/anxiety is unstable, untreated, or if current significant distress exists 5

3. Manage nausea proactively - This is the most common side effect (up to 30%) and may need dose reduction 1, 4. Consider starting with food or temporary dose reduction if problematic

4. Don't combine with NRT initially - Combination varenicline + transdermal nicotine resulted in high discontinuation rates (36%) due to adverse events 4

When to Consider Referral Instead

Refer to GP or specialist if:

• Patient has unstable or untreated depression/anxiety
• History of psychosis, mania, or bipolar disorder
• Recent suicidal ideation or attempts
• History of seizures (varenicline contraindicated) 1
• Patient preference for specialist management

The substantial benefits of immediate smoking cessation outweigh the minimal risks of neuropsychiatric effects in stably treated patients 1, 5. Your patient on stable mirtazapine is an appropriate candidate for varenicline initiation in primary care with appropriate monitoring.