Metformin doesn't typically cause blood pressure to plummet and lead to hypoglycemia, but it can—and that can cause headaches. "Metformin alone should not cause hypoglycemia,” Rodriguez explains. But “when we see headaches, it’s usually in a patient on a combination of medications that can drop blood sugars too low.” If you’re experiencing an abnormal amount of headaches or an abnormal type of headache, talk to your doctor about adjusting your medications.
Hypertension is rarely accompanied by symptoms, and its identification is usually through screening, or when seeking healthcare for an unrelated problem. Some people with high blood pressure report headaches (particularly at the back of the head and in the morning), as well as lightheadedness, vertigo, tinnitus (buzzing or hissing in the ears), altered vision or fainting episodes. These symptoms, however, might be related to associated anxiety rather than the high blood pressure itself.
Much of the disease burden of high blood pressure is experienced by people who are not labeled as hypertensive. Consequently, population strategies are required to reduce the consequences of high blood pressure and reduce the need for antihypertensive medications. Lifestyle changes are recommended to lower blood pressure, before starting medications. The 2004 British Hypertension Society guidelines proposed lifestyle changes consistent with those outlined by the US National High BP Education Program in 2002 for the primary prevention of hypertension:
The FDA most recently revised its prescribing information on metformin in 2016. Current advice is that metformin is contraindicated in people with 1) severe renal impairment (estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m2); 2) known hypersensitivity to metformin; or 3) acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma. Warnings are also given regarding the use of metformin in less severe renal impairment, people aged 65 years old or greater, hypoxic states (e.g., acute congestive heart failure), excessive alcohol intake, hepatic impairment, concomitant use of certain drugs (e.g. carbonic anhydrase inhibitors such as topiramate), surgery and other procedures, or in people having a radiological study with administration of an iodinated contrast agent. Metformin is recommended to be temporarily discontinued before any procedure involving use of iodinated contrast agents, (such as a contrast-enhanced CT scan or angiogram) due to the increased risk of lactic acidosis resulting from impaired renal function; metformin can be resumed after two days after contrast administration, if renal function is adequate and stable. It is recommended that all people receiving metformin should have their renal function (eGFR) measured at least annually and more frequently in those at higher risk of developing renal impairment.