nicotine, it is the addicting factor of cigarettes and it is what get's you hooked.
tar, It is the same as what they use to pave streets, it covers the lining of your lungs and covers the cilia, affecting your ability to clean out your lungs and breathe better, this can result in more lung problems and not being able to get over chest/ congestion related illnesses.
carcinogens, they lead to tons of different kinds of cancer.
headache
dizziness
loss of appetite
burning sensation/ throat irritation.
gum disease
not being able to get over illnesses that correlate to your respiratory system
lung cancer and mouth cancer
addiction
migraines