Offering free nicotine patches or intensive counselling to smokers calling the English NHS helpline does not help them quit, a study in the BMJ says.
University of Nottingham researchers found that this additional support - on top of what is already offered - had no effect on numbers giving up smoking.
More than 2,500 smokers were followed up over one year.
The Department of Health said it would not now offer any extra services.
The Department of Health and the UK Centre for Tobacco Control Studies, in Nottingham, funded the study to find out if the support offered currently by the NHS Smoking Helpline could be improved.
The smokers in the study were split into four groups.
The first received standard support in the form of NHS Stop Smoking Services advice, letters, emails, text messages and access to a helpline.
The second group received the same support but were also offered free nicotine replacement therapy (NRT) in the form of a 21-day supply of patches.
The third group received "proactive support" in the form of standard support plus extra counselling sessions and messages from helpline staff.
The fourth group received the same proactive support as the third group but with added free nicotine patches.
Participants in the study were followed up one month and six months later.
Analysis of the data showed that six months after quitting, 18.9% of the 59% who were contacted said they had managed not to smoke.
Nearly 80% of this group agree to give a breath test for carbon monoxide to prove that they had stopped smoking.
The study found no significant difference in success rates between those people offered different types of supportive counselling, or between those given nicotine replacement therapy.
Some 18.2% of those given proactive support had quit, compared with 19.6% of those who did not receive this support.
Overall, 17.7% of smokers who were offered the patches stopped smoking, compared with 20.1% of those not offered them.
Even one month after setting a quit date, no significant differences were found between the groups.
Professor Tim Coleman of the UK Centre for Tobacco Control Studies, who led the study, said the trial had shed light on how telephone helplines could be used to help smokers who wanted to stop.
"On the basis of this study, giving out free nicotine patches and more intensive telephone counselling through the English national quitline just doesn't seem to work.
"It brings into sharp relief the need to find other ways of using quitlines to help smokers give up, and so to reduce the terrible effects smoking has on people's lives and the costly burden to the NHS."
Amanda Sandford, from Action on Smoking and Health (Ash), said the study showed that standard NHS care was difficult to improve upon.
"We are fortunate in having a wide range of treatments available in this country which can be tailored to the individual needs of the smoker.
"The important thing is that people wanting to stop smoking should get professional advice.
"The 17-20% quit success rate found in this study is far higher than when trying to stop smoking on your own."
A Department of Health spokesman said the research was helpful in deciding what the helpline should offer.
"The Coleman study looked at what would happen if the helpline also offered extra services to smokers such as free nicotine patches. It found that there would be little additional benefit so we won't be adding this to the helpline."