Is there scientific evidence that e-cigarettes help people quit smoking?

Recently, some friends have been asking me about e-cigarettes and whether they can help with quitting smoking. There seems to be a lot of conflicting information online, with e-cigarette salespeople insisting that negative information is biased and that e-cigarettes can effectively aid in quitting smoking.

So, I decided to search on Baidu and found the following results:
 
It's understandable that e-cigarette salespeople might present biased information due to their vested interests. However, it seems that there is some level of public discourse regarding e-cigarettes in China, so I tried to find some academic papers with real experimental data to support the conclusions. I found two academic papers on the effects of e-cigarettes on quitting smoking. One was published in 2015 in the "Chinese Journal of Clinical Physicians" titled "A Survey of E-Cigarette Use Among Smokers in Beijing."
 
The researchers conducted a telephone survey of 1,188 smokers in Beijing. The results showed that 956 smokers completed the survey, of which 122 (12.8%) had used e-cigarettes, and 545 (57.0%) had heard of but not used e-cigarettes.

The study found that e-cigarettes can help smokers quit or reduce their smoking. Among smokers who used e-cigarettes, 8.3% had quit smoking, and 47.1% had reduced their cigarette consumption. Additionally, 15.1% of smokers reported that they took their first puff of e-cigarette later than their first cigarette in the morning.

The study also found that e-cigarettes were perceived to be relatively safe, with smokers not considering them to be addictive or having low addiction potential. Among the 121 smokers who had used e-cigarettes, most (84%) believed that e-cigarettes were not addictive or had lower addiction potential than traditional cigarettes, and over 70% believed that e-cigarettes were healthier than traditional cigarettes and posed no risk. This aligns with findings from research conducted by Maciej et al., where two-thirds of participants believed e-cigarettes were less addictive or non-addictive, while one-third thought using e-cigarettes was as addictive as traditional cigarettes. Most people (85%) did not consider e-cigarettes to be safe but believed their safety risks were much lower than those of traditional cigarettes.
 
The other paper was published in 2017 by Chen Jianhua et al. from Hunan Cancer Hospital, titled "Progress in E-Cigarette-Assisted Smoking Cessation." However, this paper primarily discussed e-cigarettes and quitting smoking by referencing foreign experimental results. The discussion included a 2010 online survey in the UK regarding e-cigarettes and a joint survey conducted in 2011 across the US, UK, Canada, and other countries, which did not yield consistent results. The former indicated that 96% of participants supported the idea that e-cigarettes helped them quit smoking, while the latter showed that while e-cigarette use significantly reduced smoking volume, the success rate of quitting smoking did not increase.

Currently, there is limited research on e-cigarettes and quitting smoking in China. I continued to search for international studies on e-cigarettes and quitting smoking, but the results did not yield a definitive conclusion. However, the collective findings tend to lean towards the idea that e-cigarettes can assist in quitting smoking.

A paper published in JAMA in 2014 indicated that a longitudinal analysis of two online surveys conducted a year apart with 949 smokers showed that the success rate of quitting smoking among e-cigarette users did not increase, and cigarette consumption did not decrease. However, the authors noted that the results relied heavily on self-reported data.

In developed economies, research results from the UK are relatively optimistic. A study published in February 2019 titled "A Randomized Trial Comparing E-Cigarettes and Nicotine Replacement Therapy" showed that after a year of tracking 886 participants, the quitting rate for e-cigarette users was 18%, compared to 9.9% for nicotine replacement therapy.
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In recent years, the smoking rate in the UK has steadily declined, which the health department attributes to the impact of e-cigarettes.
 
The FDA in the United States maintains a cautiously positive attitude towards e-cigarettes (nicotine delivery systems), describing them as new products with varying characteristics that may provide additional opportunities for health-conscious smokers interested in quitting. This includes products like e-cigarettes, but they need to demonstrate that they are safe and effective for quitting smoking and are regulated as drugs. This would allow them to be sold as prescription or over-the-counter products with medical claims for smoking cessation or related indications, ultimately reducing the likelihood of smokers suffering from the clinical consequences of continued smoking. This differs from our regulation of e-cigarettes as tobacco products.
 
New Zealand's official stance on e-cigarettes is more supportive, having established an official guidance website to promote a smoke-free New Zealand by 2025. They have also recorded expert guidance videos on e-cigarettes as smoking alternatives.

In summary, while there is still no definitive conclusion globally regarding e-cigarettes and quitting smoking, a significant amount of longitudinal research suggests that e-cigarettes can assist people in quitting smoking. Although it cannot guarantee individual success in quitting after using e-cigarettes, from a broader perspective, using e-cigarettes greatly increases the probability of quitting successfully. Of course, the marketing of e-cigarettes as a "quit smoking miracle" may not be entirely appropriate, as quitting smoking with e-cigarettes still carries a considerable failure rate. Considering that there is substantial research indicating that the harm of e-cigarettes to the human body is far less than that of traditional cigarettes, using e-cigarettes as a quitting option is worth considering.