Medication that helps smokers to quit is safe for use by people with chronic lung conditions, research suggests.
Experts say smokers with smoking-related diseases should be prescribed the drug to stop their illness from progressing.
Doctors have previously been reticent to give the drug to these patients because of reported links to heart disease and depression.
Researchers say they found no evidence of such a link and that concerns are unwarranted.
Varenicline is the most effective medication to help smokers quit, but previous reports have suggested that users may be more likely to suffer a heart attack.
The drug – also known as Champix or Chantix – has also been linked to depression, self-harm and suicide.
No heart risk
A study of more than 14,000 people with chronic obstructive pulmonary disorder, or COPD, found that those using the drug were no more likely to suffer a heart attack than those using nicotine replacement therapies.
Treatment did not affect their risk of depression or self-harm either, researchers say.
"Varenicline is a highly effective anti-smoking drug so it is reassuring that our findings have confirmed that it is safe for use in patients with COPD," says Professor Aziz Sheikh.
COPD is a group of lung conditions that are usually associated with tobacco smoking, including emphysema and chronic bronchitis.
The diseases are caused by damage to the lungs that results in severe breathing difficulties and a persistent cough.
"COPD is irreversible and worsens with time. The only proven way to stop the illness from progressing is to quit tobacco smoking," says Professor Daniel Kotz.
More than a million people in the UK are affected by COPD and cases are rising. The costs of treating the condition are expected to top £2.5 billion by 2030.
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Daniel Kotz et al. Cardiovascular and neuropsychiatric risks of varenicline and bupropion in smokers with chronic obstructive pulmonary disease, Thorax (2017). DOI: 10.1136/thoraxjnl-2017-210067