why does black tea raise my blood pressure ---- isint tea a diuretic ????

Some teas have caffeine in them. Yes tea and coffee are suppose to a diuretic effect.Green tea has caffeine also but only a small amount.

There are three closes related and chemically vvery similar alkaloids in the xanthine family, theophylline, the0bromine and caffeine. Theophylline (from the word TEA) is prevalent in TEA (surprise!!!!:D)
It is a potent antiasthmatic and increases the strength of smooth muscle contractions...like those in the heart. Thus the increased heart contraction can raise BP. It also speeds up the heartrate. For me, tea seems to induce copious sweating...which doesn't occur with hot coffee???

The other xanthine, the0bromine, is the main alkaloid of chocolate.

The three chemicals seem to be fairly addictive to boot? :D

Thank you for this information. Apart from having high BP I also have asthma, always feel able to breathe better after my cup of black tea, thought it was from sitting and resting. Now I know better. Thanks.