Test cyp, Tren ace and Tren E are all known for doing this from time to time. I don't have a 100% positive answer for you, as to why these specific compounds are more likely to cause "tren cough". I can say that it is probably something in the solvents trying to escape your body, using the lungs to exit. This is still speculation, but no one has a definitive answer. What I can tell you is, the best way to avoid it is to try to inject very slowly. I have gotten the cough more times than I would care to remember. At times, it's been bad enough to bring me to my knees lol. Wish I had a better answer for you. All I can tell you is it's all part of the fun of being a bodybuilder! ;)