When a single drug doesn't sort out a health issue, doctors tend to throw two at the problem. So medicine came up with the idea of hypertensive drug 'teams'. A firm favourite is a thiazide diuretic (the oldest mainstay of hypertension treatment) combined with a beta-blocker. Other combinations include a diuretic with an ACE inhibitor (such as captopril), an alpha-blocker (like prazosin) or an angiotensin-II receptor antagonist (such as losartan). ACE inhibitors are also paired up with calcium antagonists. These teams came about after initial studies showed that these drug combinations worked better than diuretics alone (Am Heart J, 1995; 130: 359-66).
Nowadays, it is a rare doctor who just relies on one drug to knock high blood pressure on the head. Of the five million people in Britain taking antihypertensive drugs, more than a third take a diuretic-beta-blocker combo.
Thiazide diuretics reduce sodium and water. They are alone among the diuretics in also widening the blood vessels.
Beta-blockers stop the effects of adrenaline (epinephrine) on beta-receptors, slowing the nerve impulses travelling through the heart so that it doesn't need to work so hard for blood and oxygen. Beta-blockers also block the receptors responsible for heart rate and a strong heartbeat.
The problem with taking two drugs is the potential for multiplying side-effects. The UK National Institute for Clinical Excellence (NICE) pooled the results of seven studies (more than 70,000 patients) and found that the diuretic-beta-blocker combination increases the risk of diabetes by 20 per cent - to 0.2 per cent per year. Although doctors call this a 'minimal risk', it represents 6666 new cases of diabetes every year.
In a study of drug side-effects to 'polypharmacy', diuretics combined with beta-blockers were among the eight most frequent culprits (Scand J Prim Health Care, 2003; 21: 153-8).
Diabetes is only the latest side-effect of the supposedly safest hypertension drugs - so much so that three out of every 100 patients quit taking the drugs due to side-effects (Pharmacotherapy, 2001; 21: 940-53). Other adverse effects of diuretics include dizziness on standing (low blood pressure), blood disorders, skin reactions, impotence, gout, pancreatitis, and depletion of many important nutrients, such as potassium, magnesium, coenzyme Q10 and zinc. Diuretics can also lead to kidney cancer. Ironically, diuretics can be especially problematical in those with heart disease (J Cardiovasc Pharmacol, 1990; 16: 58-63). It also causes the problem it's meant to prevent - low blood pressure can lead to potentially fatal cardiovascular problems (Ann Intern Med, 2002; 136: 438-48).
As for beta-blockers, they can cause dryness of the mouth, eyes and skin, wheezing, breathing difficulties or shortness of breath, slow heartbeat, sleep problems, swelling of the hands and feet, intestinal problems like diarrhoea or constipation, vomiting, back or joint pain, impotence, skin rash, sore throat, depression, memory loss, confusion and even hallucinations. They can also cause angina if you stop taking them abruptly.
Don't take the following drugs in combination:
* a beta-blocker and an alpha-adrenoceptor agonist, such as clonidine (Catapres) - this can increase blood pressure
* a beta-blocker and an ACE inhibitor - no better than one
* an alpha-adrenoceptor agonist and an alpha-blocker, a diuretic or a calcium antagonist - again, no better than one
* a beta-blocker with verapamil or diltiazem - can cause heart failure
* a calcium antagonist and an alpha-blocker, which may cause severely low blood pressure
* combination diuretics with potassium - they react with other drugs like ACE inhibitors and painkillers. Take your potassium separately
* Diuretics with HRT or the Pill - the hormones in both work to inhibit the diuretic effect (Am Fam Physicians, 1997; 56: 1275).