Ashwagandha should not cause high blood pressure but instead it could lower your blood pressure instead.
If you suffer from low blood pressure then you might not want to risk taking Ashwagandha because it cause a dangerously low blood pressure drop.
Also if you suffer from high blood pressure the Ashwagandha could interfere with medications used to treat your high blood pressure.
So if you have any of those conditions it's best to speak with a doctor before taking Ashwagandha.
Some people might experience side effects as well when taking Ashwagandha such as headache, sleepiness, and stomach upset.