Natrum Muriaticum is Latin name of Chloride of Sodium, which is actually common edible salt. Like all other homeopathic medicines, lower and higher potencies of Natrum Muriaticum too have effects opposite to each other. It is used for hypotension as well as hypertension in lower and higher potencies respectively. I have used it in various potencies and observed that Natrum Muriaticum 3X raises the blood pressure in 30 to 40 minutes, 6X raises it less than that, 30C does not significantly change the blood pressure while 200C lowers it in 30 to 40 minutes. The choice of potency would thus depend on what results you wish to achieve. Leaving alone the chemical composition, basic characteristic of common salt is warm-wet. In crude form (and lower potencies) it tends to raise the blood pressure for a short while and also creates some warmth in the body. Based on these observations, I consider Natrum Muriaticum 3X a good medicine for temporary relief of hypotension. I am saying "temporary relief" because unless cause of hypotension is removed, lasting relief cannot be achieved.
Use of Natrum Muriaticum 200C is far more complex than its lower potencies. In 30C and above Natrum Muriaticum tends to neutralize Sodium Chloride in the body and thus lower the blood pressure but should it be used in all cases of hypertension has a big question mark. Many homeopaths make the mistake of using it in most cases of hypertension, which is not right because cause of hypertension is not always the excess of salt or heat. It might work for essential hypertension because one of the causes is excessive heat and some dryness in the body but not when hypertension is due to rigidity of blood vessels or cold in the body. One of the causes of rigidity of blood vessels is excess of cold in the body that can be verified by checking the pulse and other symptoms, but this is not recognized by modern medical science. Anyway, if this be the situation, using Natrum Muriaticum 200C might spoil the case. This is because higher potencies of Natrum Muriaticum have the characteristics opposite to it lower potencies.
I have seen a case of diabetes with hypertension where Natrum Muriaticum 200C was used though infrequently yet the symptoms gradually worsened. After every dose the blood pressure fell by some points but returned to previous or slightly higher value after a day or two. Higher value of blood pressure was in fact due to excess of cold in the body, which could not be understood at that time. In fact, the person needed warmth but 200C did the opposite. Lower potency would have gradually given warmth to the body and helped in regaining elasticity of the blood vessels and ultimately brought the blood pressure down. When the mistake was realized, it was already too late. This experience became handy in treating other similar cases. So don’t take the choice of potency too easy and be very, very careful in using Natrum Muriaticum. In certain circumstances its frequent repetition might cause serious complications. Repeat it only when absolutely essential and be sure of what results you wish to achieve.