Hello! Welcome and thank you for asking on HCM! I read your question carefully and would explain that the red gritty substance may be just blood from the irritation of the gastric mucosa (gastritis or ulcers). You should know that different medications can cause irritation and inflammation of the gastric mucusa leading to bleeding associated to vomiting. You should consult with your GP for a careful physical examination and a fibrogastroscopy to exclude possible gastritis or even gastric ulcer. Hope to have been helpful! Best wishes, Dr. Aida