Q I have a problem with my left knee, which I believe is arthritis. I don’t want an operation and have heard that glucosamine, chondroitin and MSM (methyl-sulphonyl-methane) taken together are beneficial. Is there any truth in this? BC from west London

A I believe so. These substances are compounds thought to help build cartilage and stop the joints breaking down. I often prescribe glucosamine to patients with painful joints, and they report significant improvement.

Many orthopaedic consultants are also recommending this, although the scientific evidence is limited. The worst they will do is nothing, but you may find relief without side effects, so give them a go for between four and eight weeks.

Q I suffer from thirst, mostly in the evenings. I eat mainly fresh food, use no added salt and test negative for diabetes. Any suggestions? AR from Shoreham-by-Sea, West Sussex

A Make sure you have also had your kidney function tested, since kidney problems can cause significant thirst. If this is clear, drink more water.

Other common causes include eating disorders, taking diuretics (tablets that promote urination) or blood pressure tablets (which contain diuretics), and excessive sweating during exercise. Your GP should also test you for hyperparathyroidism, which can lead to high calcium levels in the blood and make you thirsty.

Q I’m going to America for a week soon. Previously after a long-haul flight I’ve suffered vertigo, putting me out of action for the first day of my holiday. Any advice? SP from Doncaster

A Alterations in air pressure can occasionally trigger this problem and you will probably benefit from taking some treatment the day you fly. Examples of prescribed medication for this include cinnarizine and betahistine, which are types of histamine used to treat nausea and vertigo. Ask your doctor to prescribe some.

If nausea is a main symptom, an acupressure wristband may provide some relief.

All questions are answered by a practising doctor. To consult Dr Know, e-mail drknow@sunday-times.co.uk . E-mails cannot be replied to individually

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