Up to 40% of patients taking clonidine (Catapres) will experience dry mouth and about a third will have drowsiness, headache, and sleepiness. Other common side effects include constipation, dizziness, and local skin reactions with use of the Catapres-TTS skin patch. Reserpine use is linked with possible side effects including nightmares, stuffy nose, depression, and an inability to fall asleep. Diarrhea and heartburn are also possible. Guanadrel and guanethidine can cause diarrhea and other gastrointestinal issues – as well as dizziness and drowsiness.

The guidelines also redefined the various categories of hypertension. It eliminated the category of prehypertension, which had been defined as systolic blood pressure of 120 to 139 mm Hg or diastolic pressure (the lower number in a reading) of 80 to 89 mm Hg. Instead, people with those readings are now categorized as having either elevated pressure (120 to 129 systolic and less than 80 diastolic) or Stage 1 hypertension (130 to 139 systolic or 80 to 89 diastolic).
Dizziness : While dizziness can be a side effect of some blood pressure medications, it is not caused by high blood pressure. However, dizziness should not be ignored, especially if the onset is sudden. Sudden dizziness, loss of balance or coordination and trouble walking are all warning signs of a stroke. High blood pressure is a leading risk factor for stroke.
Do not attempt to lower extremely elevated blood pressure in yourself or someone else. While the goal is to reduce blood pressure before additional complications develop, blood pressure should be reduced over the course of hours to days, depending on severity. It is important not to lower blood pressure too quickly, because rapid blood pressure reductions can cut off the supply of blood to the brain, leading to brain damage or death. 

Cut down on salt. As you get older, the body and blood pressure become more sensitive to salt (sodium), so you may need to watch how much salt is in your diet. Most of the salt comes from processed foods (for example, soup and baked goods). A low-salt diet, such as the DASH diet, might help lower your blood pressure. Talk with your doctor about eating less salt.
Many mechanisms have been proposed to account for the rise in peripheral resistance in hypertension. Most evidence implicates either disturbances in the kidneys' salt and water handling (particularly abnormalities in the intrarenal renin–angiotensin system)[61] or abnormalities of the sympathetic nervous system.[62] These mechanisms are not mutually exclusive and it is likely that both contribute to some extent in most cases of essential hypertension. It has also been suggested that endothelial dysfunction and vascular inflammation may also contribute to increased peripheral resistance and vascular damage in hypertension.[63][64] Interleukin 17 has garnered interest for its role in increasing the production of several other immune system chemical signals thought to be involved in hypertension such as tumor necrosis factor alpha, interleukin 1, interleukin 6, and interleukin 8.[65]
Often, hypertension can improve with lifestyle changes. In some cases, high blood pressure can go down to normal levels with only lifestyle modifications, particularly if you have stage 1 hypertension (systolic blood pressure of 130 mmHg to 159 mmHg, or diastolic blood pressure 80 mmHg to 99 mmHg), or if you have elevated blood pressure (systolic blood of 120 mmHg to 129 mmHg and diastolic less than 80 mmHg).
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