Hi
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Dark grey or brown matter can be old blood or blood that has reacted with acid in your stomach. There is a possibility you have bleeding gastric ulcer or esophageal varices. Take Omeprazole empty stomach in morning and an antacid gel at bedtime. Refrain from smoking, alcohol, fuzzy drinks and spicy food. Consult a gastroenterologist. Take care!
Let me add that I do not smoke cigarettes, I used to for a for a little while (about 2 years), but quit about 3-4 years ago.I feel that it is tar/resin that has just built up over years of abuse, especially considering I am not physically active in the least bit. And I haven't had this issue with the dark phlegm long, maybe about 2 months and I really don't have a chronic cough . I took a total cold turkey break for about 20 days when the amount coughed up seemed to have 'peaked' about 3-4 weeks ago, and the amount seemed to slowly lessen each day. til it was pretty much happening ever other day and getting less and less.... Well I smoked again for the past two days and ended the break and i woke up this morning and coughed up one big 'chunk' of that clear phlegm with dark pieces, and for the rest of the day I've been pretty much clear.. I don't get what you mean there is nothing in marijuana to make you do that? From what I have seen there are pretty decent amounts of resin that come from burning/smoking marijuana, specifically high quality marijuana, and by looking at the inside of a thoroughly used marijuana pipe of any kind. I'm going to give it a bit longer until I go see a Dr, as I have no insurance, and im going to give the weed a total break for a few months, and perhaps start to get some exercise.
Being a chain smoker, and moderate marijuana user, I can say that I often have the same thing. I also know other people who do.
As a former smoker of 2 years id say no that's not normal because there's nothing in the marijuana to make you do that it has to be something else that you are doing mabey you should go to a clinic or a dr. And have that checked out