Aspirin is an antihistamine.
If I left this statement there, there would be all kinds of contradictions from armchair doctors (and perhaps a few actual doctors) who don't know what an antihistamine really is - because they don't know or understand what histamine is. And there has to be histamine or else there can't be an antihistamine.
So now that I have everyone's attention, I'll explain.
Histamine is a neurotransmitter that regulates the water levels in the body. The general make-up of the body is around 75% water with the blood being 94% water. There has to be this much water because every function depends on it.
When you become dehydrated the blood loses 8% of its water volume and this is what causes the blood to thicken. At the same time, the vessels tighten up to compensate for the water loss. This increases the workload on the heart which must increase the blood pressure to maintain efficient circulation.
Another part of the process involves reverse osmosis and how it filters salt water to inject fresh water back into the dehydrated calls - the increase in blood pressure is needed for this function.
Blood thinners such as aspirin are prescribed to ease the workload on the heart by reducing the viscosity of the blood. Other medications work to relax the vessels (or open them up) to allow the thickened blood to flow through easier.
Diuretics work a different way than people think. They don't remove excess water and salt from the vessels because there is no excess water and salt in the vessels - again, dehydration has reduced the water volume by 8% and this is why it thickens. If the theory about too much water were true then the blood would be so watery that it would never thicken, nor would it cause the vessels to constrict.
The way diuretics work is they reduce the volume of water and salt that sits outside the cells (the same water and salt that reverse osmosis is filtering and injecting into the dehydrated cells). By injecting water into the cells, it alleviates the difference in water volume between the inside and outside of the cells. Diuretics remove this water and salt mixture which also alleviates the difference in water levels. Only instead of injecting it into the cells where it needs to be, it removes it from the body.
When the water levels become more aligned not as much pressure is needed for the injection process and the overall blood pressure goes down. Diuretics get the credit for this, but it's not part of a healthy process because by removing water from the body instead of correcting the insufficient water levels it solves nothing - dehydration is still a problem and eventually, other medications will be prescribed because the diuretics will become ineffective.
You can never correct dehydration by removing the water.