Caffeine has a wide variety of effects in the body. Mechanistically, some of the effects are direct (such as Caffeine acting as an Adenosine Antagonist, the molecule literally blocks the receptor) and others are indirect (any effects on dopamine are ‘downstream’ of the reaction with adenosine, like the latter aspects of a Domino cascade). When tolerance develops to caffeine
Caffeine is a performance-enhancing drug that’s legal, cheap, and easy to get: chances are you had some this morning. More importantly, it actually does make you better at sports, which is more than you can say for a lot of supplements marketed to athletes. You just have to know how to use it strategically.
If you are older, and are taking blood thinners, if you have a disease or condition that keeps your blood from clotting properly, or if you are soon having surgery, you may find yourself with some unexpected dietary restrictions. Onions and garlic, especially raw onions and garlic, are off the plate.
Onions have never been a risk when I looked. Garlic was not recommended, but my experience to date says that’s rubbish. I consume a fair bit of garlic, and my dose has not changed in years. It might be different for others, but generally unlikely.