Earlier this year, Michael Gove claimed Britain’s had enough of experts. Now I don’t agree with Gove on much, but when it comes to e-cigarettes, he may have a point. We’re bombarded with stories about these products, but most just add to the confusion, with perceptions of vaping risks rising year on year. Just recently the Sun informed us that experts are saying “e-cigs are just as bad for your heart as smoking fags”, but read a couple lines down and you’ll find other experts reasserting the claim that e-cigarettes are 95% safer than tobacco. So which is it? Why can’t the scientists agree? And will they ever?

Cochrane is a global non-profit group that reviews all the evidence on healthcare interventions and summarises the findings so people making important decisions – you, your doctor, the people who write medical guidelines – can use unbiased information to make difficult choices without having to first read every study out there. This week, the latest Cochrane review of e-cigarettes was published. I’m its lead author. While our conclusions are limited because there aren’t many high quality studies available yet, overall the evidence suggests that (1) e-cigarettes with nicotine can help people quit smoking, (2) they don’t seem to have any serious side effects in the short- to mid- term (up to 2 years), and (3) in some cases, switching to them leads to changes in your blood and breath that are consistent with the changes you’d see in people who give up smoking altogether.

This is good news. But other systematic reviews and studies have drawn very different conclusions, and I’m going to try to shed some light why that is.

Can e-cigarettes help people quit?

Our Cochrane review (and others, like this one published in PloS One) suggest they can. But a review published in the Lancet Respiratory Medicine earlier this year, which received a lot of attention, suggests they actually make it harder. The reason for this difference is the types of studies the authors include.

Randomized controlled trials are the best way to see if a treatment works. As Ben Goldacre, author of Bad Science, explains, by randomly assigning people to one intervention or another and measuring the outcome in the same way across both groups, you can rule out alternative explanations for differences between groups. The reviews that find e-cigarettes help people quit smoking only include randomized controlled trials. The studies (like this one and this one) that find that e-cigarettes stop people from quitting aren’t randomized controlled trials - instead they survey smokers and ask if they are using e-cigarettes. Then, some months later, they ask the same people if they are still smoking. We don’t know if the results from these studies reflect the effect of vaping, or if something else about the vapers makes it harder for them to quit. For example, it might be reasonable to imagine they are more dependent smokers, which is why they vape as well as using regular cigarettes. This would make quitting harder.

Are they safe?

The issue here isn’t so much the study type, but the way you ask the question. By ‘safe,’ do you mean completely without risk? No, they’re not – not much is. We’ve seen stories about people catching fire and puppies with nicotine poisoning. Plus, in general, it’s not a great idea to inhale chemicals into your lungs if you can avoid it. Experts basically agree on that – I’ve yet to come across a tobacco researcher or policy maker who would recommend you start using e-cigarettes if you aren’t already a smoker.

The crucial question here is – safe compared to what? Cigarettes are uniquely deadly. They kill one in two people who use them regularly. So, if you’re asking whether e-cigarettes are safer than regular cigarettes, most experts would, after briefly hesitating, lean on the side of yes. The hesitation is there because e-cigarettes are new to the scene. We don’t know their long-term safety profile, so we have to look for clues elsewhere – for example, studies that measure side effects of short-term use (results from these are promising) and studies about how e-cigarettes affect your blood, lungs and heart. Interpreting these measures is complicated. For example, a recent study found that vaping affects the same blood vessel in your heart as smoking regular cigarettes. This isn’t necessarily surprising – we know nicotine, the active agent in both, affects this vessel. We also know that nicotine isn’t responsible for the harms associated with smoking. So how to interpret these results? The gamut of expert reactions ran from “[e-cigarettes are] far more dangerous than people realise” to “vaping carries a fraction of the risk of smoking.” When it comes to long-term safety, experts are making their best guesses in the absence of solid data, and that’s where room for disagreement creeps in.

So what’s next?

The good news is there’s lots of research going on – finally. The most recent update of the Cochrane review found 26 studies in the pipeline that will help answer questions about the safety and effect of using e-cigarettes to quit smoking. The more studies we have looking at a question, the more certain we can be about the answer. The irony is that until we have the answer, narrow interpretations of the results of individual studies risk doing further harm, undermining public confidence in science and possibly discouraging quit attempts. Fundamentally, tobacco researchers on both sides of the argument want the same thing – to reduce death and disease. We’re in the same boat. If you’re reading this as a member of the public, please don’t be put off by the conflicting headlines – we all agree cigarettes are bad for you, most of us agree vaping is probably much safer than smoking regular cigarettes, and if you’re a smoker we all really want our research to help you to quit. Don’t let us get in the way.

Jamie Hartmann-Boyce is an author and editor of the Cochrane Tobacco Addiction group, based at the Nuffield Department of Primary Care Health Sciences, University of Oxford, Radcliffe Observatory Quarter, Oxford, UK. She works as part of the Health Behaviours team, reviewing the most recent evidence to help people stop smoking and manage their weight. You can find her on twitter at @jhb19. Her words stated and expressed in this blog are entirely personal, and do not represent any official views or opinions of Cochrane.