If you trawl through the web looking for advice about 'sensible' or 'safe' limits for drinking coffee, you'll find a lot of contradictory advice. Once you've eliminated the 'extreme' and 'downright cranky' views however, you'll find that there seems to be general agreement on the following:
1. Drinking coffee, in moderate quantities (see below), has no harmful effects and might well be beneficial.
2. The definition of 'moderate' has to take into account both the size of the cups/mugs and the strength of the coffee. However, based upon a heaped spoonful of instant coffee being regarded as the basis for a single 'cup', there seems to be agreement that 3 cups per day can be regarded as both 'moderate' and 'safe'.
Stating that virtually all responsible authorities agree that 3 cups per day is 'OK' is not the same, however, as saying that they all agree that more than 3 cups is harmful. Many 'experts' see no reason to be concerned about consumption levels at much higher levels (although some prefer to recommend a maximum of 3 cups) but there still seem to be a number of unanswered questions about possible health hazards.
While coffee consumption might not directly lead to hypertension, it should be remembered that caffeine is a diuretic which can lead to dehydration of the body. This, in turn, results in 'thickening' of the blood which can be a cause of hypertension.
Chris
PS: At college I drank 20 to 30 mugs of coffee a day, usually made with 2 or 3 heaped spoonfuls of Nescafe (i.e. effectively between 40 and 90 'normal' cups per day) and, although it's now 30 years later, I've not dropped dead yet!