Stop there.
Get a medical check up because this drug if used in large (which you will be using) doses then you can or will have heart problems. This can be the result of an underlying heart condition. So, look at family history, ask your GP for a BP and heart check up (ECG if possible, they're quick and easy if they have the equipment) and go from there.
Secondary to this, you will want to find information from a legitimate source at the moment you have a bunch of random internet people telling you how to do it, what to look out for and what side effect they (or someone they know) felt. This may or may not be true (did you hear about the lesbian blogger that got arrested in Syria who turned out to be a 40 year old American guy?), so I'd take it all with a massive grain of salt, hell even my comments. Find a good doctor, or ask for recommendations, talk to them about what you're planning to do. They won't give you a prescription, but they *should* talk to you about potential issues, how to protect any organs that might be effected by the drugs themselves.
Like a lot of cold and flu medications that contain decongestants, this shouldn't be used if you've got high blood pressure (do you even know what your is?), heart conditions or a family history of CVA or TIAs.