Very few studies have been done because it is such a fast-changing area. A doctor in New Zealand, Dr. Bullen, conducted a study that showed that e-cigarettes were as effective as nicotine replacement therapy. What we're seeing two or three years down the line with nicotine replacement therapies, especially over-the-counter ones, which are available without a prescription or any counselling, is that they are not very good.
It will be necessary to rely on retrospective studies, with all the limitations and biases associated with them. I don't think we have any other choice given how quickly this market is changing.
In fact, I was recently asked to be part of a prospective study. I said no because I didn't think it would be ethical. It would be unethical of me not to let a patient use an e-cigarette immediately following a heart attack or a 10-day stay in hospital for chronic lung disease exacerbation. In those situations, a patient can be allowed to smoke a nicotine-free e-cigarette—they do exist—or even a placebo electronic cigarette.
It will be necessary to rely on retrospective studies. If we manage to conduct a study on a significant number of patients and everyone arrives at the same findings, I think it would be reliable.