(At the time, Juul, the top seller in the United States, was not available in England. Juul has much higher nicotine concentrations — either 59 milligrams or 35 milligrams.)

All the participants had individual latitude within their study groups to closely approximate real-life scenarios. When the vapers finished their bottle of nicotine liquid, they could choose whichever flavor and nicotine strength to purchase.

The people using nicotine replacement therapy could select from an array of products, including the patch, gum, lozenge and nasal spray. They were even encouraged to combine them; most did so, typically opting for the patch and an oral therapy.

Because self-reports of smoking abstinence are not considered reliable, researchers measured the quantities of carbon monoxide in the participants’ breath, a more precise validation.

Dr. Maciej Goniewicz, a co-author of the British study who is now a pharmacologist at the Roswell Park Comprehensive Cancer Center in Buffalo, N.Y., said that the success of the e-cigarettes most likely reflects a combination of factors:

“It’s about the method of delivery, the quantity of nicotine and the user’s behavior,” he said. “E-cigarettes have the advantage that the user decides how and when to puff. Nicotine replacement therapy products have specific instructions, which are different for different products.”

Dr. Benowitz noted that the higher quit rates and compliance among e-cigarette users could be additionally explained because those subjects expressed more satisfaction with the devices than did the other group with their products.

In their editorial, Drs. Borrelli and O’Connor pointed to other research on smoking cessation therapies: In one study nicotine-replacement therapy and the antidepressant buproprion (Wellbutrin) achieved slightly higher abstinence rates than did e-cigarettes in this latest trial. The prescription drug varenicline (Chantix) has performed even moderately better. Moreover, these products have been proven safe, they said.