From another forum
I'm certainly glad to hear that you haven't had any major health consequences of mixing EC and Pristiq yet. Unfortunately, that doesn't mean that you're in the clear, and here's why. Pristiq is an SNRI, or Serotonin and Norepinephrine Reuptake Inhibitor. It increases the serotonin and norepinephrine input to your nervous system (specifically, each time those two chemicals get released to stimulate a neuron, it blocks the body's enzymes that break them down, making the signals last longer). Ephedrine's effects are more numerous and less well understood, but we know that among them it enhances the release of norepinephrine and increases the activity of norepinephrine receptors. By combining these drugs, you end up flooding your neurons with norepinephrine and disabling the body's ability to wash it out. Marinating your nervous system in adrenaline can be a bad thing acutely because it can kill you (unrestrained hypertension with stroke or cerebral aneurysm, sudden cardiac death, etc). However, it can also be dangerous chronically, because keeping your body in the stressed fight or flight state can cause slow, silent damage to your heart and circulatory system (specifically myocardial necrosis and valvular damage, potentially but not necessarily leading to congestive heart failure aka inability of the heart to adequately pump blood), which only makes itself known to you when the heart can finally no longer compensate for all its chronic injury.
Additionally, taking both of these drugs together puts you at an increased risk for cardiac arrhythmia (again, because of the massive excess of norepinephrine activity). Arrhythmia is something that does not necessarily produce any physical symptoms and is also something that can come and go at will. My point being, unless you have your finger on your pulse all day (and even then, because the disturbance in heart rhythm is often subtle and hard to pick out), the drugs may be moving you in and out on normal cardiac rhythm without you even noticing. This is problematic because the 'benign' asymptomatic arrhythmias can sometimes transform into life threatening/ending rhythms, but also because they mess with the blood flow through the heart and increase your risk of forming clots in the heart, which can then travel up your carotid arteries and block off the blood flow your brain, causing a stroke.
In summary, I'm afraid the answer to your question is no. It's entirely possible to take Ephedrine and Pristiq for months or even years without noticing any unusual symptoms, and then end up suffering a heart attack, stroke, sudden death, etc. It's also possible that you may be slowly developing injury that will lead to long term health issues such as heart failure in the future, and that you've yet to notice because your heart hasn't become sufficiently injured to start producing symptoms.