Green tea.
yes, in fact both caffeine and aspirin are the main ingredients in a well-known migraine/headache medicine.
The biggest use of caffeine is as a stimulant drug. People drink coffee and other drinks with caffeine to stay awake. Doctors sometimes use caffeine as a medicine like for example: headaches and head pain. Caffeine is sometimes given to people after lumber puncture, caffeine was found to relieve hunger so it was used for loss. That did not last because people were using to much. Caffeine can be a very dangerous drug when not used in the right way. Caffeine also has medicinal properties it is used in many over the counter medicines. Caffeine can help to alleviate headaches and cramps.
By truckers
Yes - cola drinks contain caffeine.
A tree mentioned in the film "Medicine Man". Its bark is described as having 3% pure caffeine.
Coffee, tea, chocolate, some medicine, energy drinks, some ice creams. That sort of stuff.
into the bloodstream
caffeine
No, helium is not used in medicine.
No, zebras are not used in medicine.
Uranium is not used in medicine.