I did gain about 5 lbs. when I switched. I think for me it has to do with decreasing the amount of nicotine intake. I started out at 10 mg which wasn't enough to get me off the analogs. I bumped it up to 14 mg and that was great but my favorite juice right now is a 12 and that's when the gain kicked in. Nicotine is the substance in cigarettes that causes weight loss. I'm sure you've heard the old stories of how doctors in the 50's would prescribe smoking as an appetite suppressant to loss weight. Yikes!