Sometimes it's not wise to take health supplements.

When taken for the wrong condition

A person gaining weight due to thyroid problems might turn to weight-loss supplements. This will not help.

Glucosamine may not be useful in rheumatoid arthritis, a condition in which the immune system attacks the joints. Using it may simply delay treatment.

When they might interact with medication

Patients on blood-thinning medicine (warfarin) may want to avoid cranberry extract as this may make it more difficult to get their blood to clot if they start bleeding.

Calcium supplements may interact with some forms of antibiotics, making them less effective.

This article was first published in The Sunday Times on Apr 6, 2008.