One thing I notice in this thread is that sometimes people are talking about taking nigella seeds and sometimes nigella oil, and with the oil there is a big difference between a cold pressed nigella oil and an essential nigella oil, as essential oils are very concentrated. When I read one teaspoon of nigella oil, I assume it is the cold pressed oil, which is safe to take in teaspoon quantities. Essential oils would be measured in drops and a much smaller volume would be used. So, the different forms should be used according to that form and can't really be compared.
If you Google "nigella oil" you will see many results concerning studies on the many different properties and medicinal uses of nigella. It's an amazing and tasty herb, and I've been using it in many different foods. Today was in egg salad. I hope it has some effect on my asthma.
Maha, that's great that the hematologist is also a nutritionist. I wish more doctors would study the value of nutrients, including the properties of herbs.