There's a lot of information available about tea and health as well as vegetables and health. Most of it is very positive. However, foods and drinks generally contain many complex chemical compounds, not all of them "good for you."
Nicotine is one such compound. Nicotine is an addictive substance found in tobacco, eggplants, potatoes, cauliflower, and, according to one study, tea.
What Is Nicotine?
Nicotine is a chemical compound (C10H14N2) which has a strong impact on human and animal physiology and neurology.
A naturally occurring liquid alkaloid, it has properties related to those in caffeine. Classed as a stimulant, it can paradoxically also act as a sedative under certain conditions. Most people who experience nicotine through smoking, vaping, or nicotine patches find it relaxing. It is found in plants related to deadly nightshade including, among others, tobacco, potatoes, tomatoes, eggplant, and capsicum peppers.
Why Nicotine Is a Problem
In large doses, nicotine is very poisonous and can be fatal. According to a 2015 study looking at the impact of nicotine when it is not associated with smoking:
Nicotine poses several health hazards. There is an increased risk of cardiovascular, respiratory, gastrointestinal disorders. There is decreased immune response and it also poses ill impacts on the reproductive health. It affects the cell proliferation, oxidative stress, apoptosis, DNA mutation by various mechanisms which leads to cancer. It also affects the tumor proliferation and metastasis and causes resistance to chemo and radio therapeutic agents.
Nicotine addiction is partially responsible for cigarette addiction. A cigarette contains approximately 10 milligrams of nicotine. However, only one or two milligrams is inhaled directly when one smokes a cigarette, and only one milligram of nicotine is absorbed over the course of three hours of "passive smoking" (breathing secondhand smoke) in a room with minimal cigarette smoke.
Nicotine in Food
Nicotine occurs naturally in some foods and can get into other plant-based foods through the soil. But the amount of nicotine you'd ingest from such foods is tiny. Some people worry that the nicotine in foods could trigger a cigarette craving, but the likelihood is extremely low.
One nicotine study, for example, found that 10 grams of eggplant contains about one microgram of nicotine, while 19.2 grams of pureed tomatoes contain the same level of nicotine. It takes 1000 micrograms to equal one milligram, so you'd need to eat 10 kilograms or about 22 pounds of eggplant to take in as much nicotine as you'd get from three hours of minimal passive smoke.
Nicotine in Tea
Scientific claims surrounding the levels of nicotine in tea range from negligible/nonexistent to 285 nanograms of nicotine per gram of tea in instant tea and 100 nanograms per gram black tea (whether regular or decaf). A 1999 study on nicotine in tea and vegetables stated that "Nicotine content in tea leaves was found to be highly variable and sometimes much larger than in the Solanaceae fruits [such as eggplants, potatoes, and tomatoes]." However, a more recent study of nicotine in food found no measurable nicotine in black tea purchased at a regular grocery store (likely tea bags).
If the situation is as bad as the first study claims, then it would take over 3.5 kilograms (more than 7.7 pounds) of instant tea (which had the highest levels of nicotine in the study) to yield one microgram of nicotine (the amount you'd get from minimal secondhand smoke).
If tea does contain nicotine, the levels are very low. It is generally agreed that these levels are not nearly high enough to impact cigarette consumption or cigarette cravings. Additionally, several scientists have pointed out that the absorption of nicotine through the lungs is very different from the absorption of nicotine through digestion. Therefore, the impact on your health as a smoker, non-smoker or former smoker should be negligible, and will likely be far outweighed by tea's many health benefits.
If you're still worried about getting addicted to the nicotine that may or may not be in tea, don't be.
You're far more likely to face caffeine addiction (as well as sugar addiction if you add sugar to your tea) than you are to have any issues with nicotine in tea.
Mishra, A., Chaturvedi, P., Datta, S., Sinukumar, S., Joshi, P., & Garg, A. (2015). Harmful effects of nicotine. Indian Journal of Medical and Paediatric Oncology : Official Journal of Indian Society of Medical & Paediatric Oncology, 36(1), 24–31.
Siegmund, B. et al. Determination of the nicotine content of various edible nightshades (Solanaceae) and their products and estimation of the associated dietary nicotine intake. Journal of Agricultural and Food Chemistry. 1999 47 (8), 3113-3120.
Thräne, C. et al. Determination of nicotine in tea (Camellia sinensis) by LC–ESI–MS/MS using a modified QuEChERS method. August 2015, Volume 241, Issue 2, pp 227–232