Obviously huge quantities of anything are bad, but caffeine has virtually no downsides.
I was hospitalized for a long time because of a very serious, bad case of mumps as an adult and in the hospital I was treated they were very serious about controlling my diet so I couldn't drink coffee for a long while.
When I recovered and went back home, I started drinking the same amount of coffee I was used to, which normally wouldn't make me feel anything out of the ordinary, but because I had not been exposed to caffeine for a while, I ended up with a severe feeling of tingling in my limbs, the level of stimulation really shocked me. After a month and half (possibly a little more, I'm fuzzy on the passing of days during those times) of not drinking coffee, it was as if I had been a new coffee drinker again and my body forgot caffeine. Habitual, daily exposure can /strongly/ affect the amount of caffeine it will take for you to feel its presence at a symptomatic level, and abstaining from caffeine for a long enough period can also completely throw you back to the beginning stage.
Neither a glass of tea nor a glass of wine will kill you, but excessive consumption of just about anything can.
> Hyponatremia is the most common type of electrolyte imbalance, and is often found in older adults.[11][12] It occurs in about 20% of those admitted to hospital and 10% of people during or after an endurance sporting event.[3][5] Among those in hospital, hyponatremia is associated with an increased risk of death.[5] The economic costs of hyponatremia are estimated at $2.6 billion per annum in the United States
A woman made the headlines once for dying in a contest that involved drinking absurd amounts of water in the shortest time.
https://www.cbsnews.com/news/ten-fired-after-radio-contest-t...
The amount? two gallons, so around 7.5 liters of water. Now, spaced around an entire day (rather than in under an hour), it's unlikely to immediately kill you, but even 4 liters of anything is going to be damaging to your health long term wise.
Alcohol certainly isn't good for you even in small amounts, but neither is drinking a lot of water, tea, coffee, soda or anything else. The human body was not made to process large amount of anything every day of the week.
There is no such a thing as a substance that is "healthy" to "abuse". Unfortunately, there are too many who believe the contrary (as evidenced by the post talking about the guy drinking humongous amounts of green tea to "detox" his body)
The desire to continuously stimulate the senses through binge drinking things (which can sometimes be water, many have damaged their body by drinking excessive amounts on a daily basis) or binge eating, well, that's a mental illness in the making.
It could be there's something unique in this case, some chemical in Earl Grey isn't being properly metabolized and that's causing the issues. Investigating further could lead to some advancement in biochemistry.
In my opinion, the chances are quite small for this to lead to any significant scientific advancement, but even so, it's still worth investigating.
I stopped when my mum (a physician) pointed out that the number of tea leaves I was consuming (not deliberately, but casually) would probably cause oesophageal cancer. Perhaps she merely wanted me to vary my diet.
I'm going to assume you're not British then.