Q I take warfarin to stop clots forming on a new heart valve. I've also been taking cranberry juice for cystitis, but my doctor says they are not compatible. Why is this, and what should I take instead for my urinary infections?

A Your doctor is correct. Cranberry juice may increase the effect of the clot-preventing drug so that you may start to bleed. If you are taking cranberry juice you need more frequent blood tests to check on your clotting times. Drinking plain water instead may be better for you. If you are having frequent urine infections, take samples to your doctor for culture to find out the cause and the appropriate antibiotic to use against it.

Q I'm a woman going through the menopause. I don't want to take HRT because of the risks. What do you think of black cohosh? A friend suggested I try it.

A It is more than four years since all family doctors in Britain were advised against it by the then Committee of Safety of Medicines. This was on the basis that ten British women had reacted badly to it, seven of whom developed liver disease. Two needed transplants. Why not talk to your doctor about how best to control your menopausal symptoms? There are plenty of relatively safe and effective treatments.

Q My three-year-old grandson has serious difficulty opening his bowel. He screams in pain, doesn't pass a motion for two or more days, and when he does it is large and hard. He eats healthily and drinks plenty of fluid. What can we do?

A He may have a small tear in the anus (a fissure') that hurts a lot when the motion is coming through it. Your doctor will need to examine him to confirm it or rule it out. He may be prescribed a softening agent, like lactulose, to ease the pain, plus a soothing ointment to be used before he tries to pass stools.