People who smoke tobacco along with cannabis, such as in joints, not only do so to save money but also to increase the efficiency of inhalation.
A study says that this mixing can reduce the motivation to quit the drug and increases the risk of dependency.
While one billion people use tobacco, cannabis is used by 182 million people, according to the World Health Organisation (WHO).
"Cannabis and tobacco dependence manifest in similar ways, often making it difficult to separate these out in people who use both the drugs," said lead author Chandni Hindocha, a doctoral student at the Clinical Psychopharmacology Unit of the University College London.
The findings show that the people who mix tobacco with cannabis are less motivated to seek professional help to quit it.
The people who regularly mix tobacco with cannabis are more at risk of psychological dependence than people who use cannabis and tobacco separately, without mixing them, the researchers said.
Cannabis users who favour non-tobacco routes had 61.5 per cent higher odds of wanting professional help to use less cannabis, and 80.6 per cent higher odds of wanting help to use less tobacco, than those users who prefer tobacco routes, said the paper published in the journal Frontiers in Psychiatry.
"Our results highlight the importance of routes of administration when considering the health effects of cannabis and shows that the co-administration of tobacco and cannabis is associated with decreased motivation to cease tobacco use, and to seek help for ceasing it," noted Michael T. Lynskey, Professor at King's College London.
For the study, the team analysed responses from 33, 687 cannabis users from 18 countries in Europe, North and South America and Australia and found that the routes of administration of these drugs varied widely between the countries.
The Europeans, between 77.2 per cent and 90.9 per cent, were found to be the most inclined to combine cannabis with tobacco, compared to 51.6 per cent of the Australians and 20.7 per cent of the New Zealanders.
Tobacco routes were found to be least popular in America. Only 4.4 per cent of the Americans, 6.9 per cent of the Mexican, 7.4 per cent of the Brazilian cannabis and 16 per cent of the Canadians combined cannabis with tobacco.
In contrast, 13.2 per cent of the Canadians and 11.2 per cent of the Americans use the e-cigarette routes.
Further, the most popular tobacco route of administration for cannabis worldwide, is the joint, preferred by 93.4 per cent of users of tobacco routes.