Many people take drugs that interfere with their blood pressure pills

People who take pills to lower their blood pressure often take other drugs that reduce the pills’ effectiveness, a recent study suggests.

Researchers studied data on 521,028 adults prescribed blood pressure pills for the first time and 131,764 people taking at least four different pills to lower their blood pressure.

Roughly 18 per cent were also taking drugs that make blood pressure pills less effective, the study found. These include medicines like non-steroidal anti-inflammatory drugs (NSAIDs), acetaminophen, or hormones.

“In some cases, use of these blood pressure-interfering medications may be justified and the potential side effect of elevations in blood pressure may be acceptable to patients,” said study leader Andrew Hwang of the High Point University Fred Wilson School of Pharmacy in North Carolina.

“But in other cases . . . there may be significant opportunities to switch to alternative treatments or reassess the need for continuing the interfering treatment,” Hwang said by e-mail. “If these drugs can be discontinued, it’s possible we can reduce the prescribing cascade — that is, reduce the need for using additional medication to treat a side effect of another medication.”

Patients may not realise the risks, the findings suggest.

Among people recently prescribed blood pressure medications for the first time, 58 per cent later refilled prescriptions for drugs known to increase blood pressure, the study found.

Among people prescribed four or more blood pressure drugs, 65 per cent refilled drugs known to increase blood pressure after stepping up their blood pressure treatment regimen.

Patients who need blood pressure medicine should ask their doctor if any of the other medications they are taking might interfere, said Gunnar Gislason, a professor of cardiology at Copenhagen University Hospital Herlev and Gentofte and director of research at the Danish Heart Foundation.

And if blood pressure drugs are not working, it is important to consider not just other drugs that might influence blood pressure but also herbal medications that often are considered harmless, Gislason, who was not involved in the study, said by e-mail.

The way different drugs can increase blood pressure varies, Hwang said.

“Some drugs, such as NSAIDs and hormones, elevate blood pressure mainly by causing the body to retain excess fluid,” Hwang noted. “This effect counteracts the mechanism of some blood pressure medications like diuretics [water pills], which cause the body to get rid of fluid.”

“Other drugs can cause blood pressure elevation by constricting the blood vessels, increasing heart rate, or by a combination of mechanisms,” Hwang added. “There are also some drugs, such as acetaminophen, that we know increase blood pressure, but we don’t know how.”

The study, published in the American Journal of Hypertension, was not designed to prove whether or how certain prescription drugs might interfere with the effectiveness of blood pressure medicines or increase blood pressure.

Another limitation is that it focused only on patients who were taking prescribed medicines that can interfere with blood pressure drugs, and many painkillers like acetaminophen and naproxen are available over the counter without a prescription in the US, the study authors note.

“Although this study cannot tell us the reasons why the prescription rate of blood pressure-interfering medication is so frequent, it may explain why in [the] US population blood pressure control is still very poor,” said Liffert Vogt of Amsterdam University Medical Centre.

“Poorly controlled blood pressure [is] a major cause of heart disease and stroke,” Vogt, who was not involved in the study, said by e-mail. “For that reason, prescribing drugs that contribute to poor blood pressure control should be carefully considered.”