Nicotine doesn’t cause smoking-related diseases, such as cancers and heart disease, but it is addictive. However, there’s a common misconception that you can overdose on nicotine using e-cigarettes. But you are in no danger of poisoning yourself, nor have there been any cases of overdose from inhaling the nicotine-containing fluid that an e-cigarette vaporises, known as e-liquid. So you can use your e-cigarette as often as you need to help manage nicotine withdrawal and urges to smoke.
Much the same as with Nicotine Replacement Therapy, if you do have more nicotine than you’re used to, then you might feel a little nauseous or lightheaded, both of which pass quickly. If this happens, just reduce the level of nicotine in the e-liquid that you buy, or use the e-cigarette less.