Testosterone causes a stimulating effect that causes your blood cell count to increase and potentially thicken and cause blood clots.
The Testosterone and Testosterone Therapy causes what's known as polycythemia which increases your bodies supply of hemoglobin and hematocri.
When that supply of hemoglobin and hematocri increases it then can increase your blood pressure and cause your blood to thicken some.
If you think you have an increase in your red blood count or your blood is thickening you should see a doctor and let them know to prevent a blood clot.