[Update: it seems pretty rough on my throat, and it just does not seem strong. Maybe the nicotine concentrate is not good or something. I'm going back to the gum. ]
Nicotine is the strongest substance we know of in preventing and/or slowing Parkinson's. Surprisingly, it does not seem to cause cancer in animals, but it has caused cancer in test tube. A derivative of nicotine, "NNK" appears the be the most potent cancer causing agent in cigarettes, second-hand smoke, and chewing tobacco. NNK comes from nicotine during the curing of tobacco and during the high heat of smoking. The amount of NNK in e-cig liquids is about 1000 times less than it is in burnt cigarette smoke, and the lower temperature of e-cigs is not supposed to generate NNK from the nicotine. I bought the equivalent of 300 packs of cigarettes for $26 ($0.08 per pack) by mixing the nicotine concentrate from nicvape with VG oil from amazon (0.1 ml to 0.2 ml of 100 mg nicotine/ml concentrate with 1 ml VG oil and 0.1 ml water). Two e-cigs pens cost $13 from ebay. If you do a google search, all you can find are $40 models. The pre-mixed liquids are also expensive.
There are other carcinogens in cigarettes, but the situation is similar in regards to them. Nicotine is not safe, and may assist existing cancer and appears to have some negative effects in arteriosclerosis, but it generally regarded by health authorities to be at least 20 times safer than cigarettes, except it is still addictive.
Just mixing the liquid and taking drops of it orally would be like nicotine gum, except a lot cheaper. Mixing with DMSO can carry it through the skin....a lot cheaper than buying patches.
NNK in e-cig liquids:
1 ml e-cig liquid is about 20 cigarettes:
e-cig temperatures supposedly do not generate NNK
Amount of NNK from cigarettes