My doctor has been giving me a tranquilliser called diazepam for about the past ten years. Recently, I have noticed some of the pills have been vanishing from my bathroom cupboard.

I strongly suspect my 19-year-old daughter may have been stealing them. Is this likely? I can’t understand why she would want to pinch them.

Well, diazepam, also known as Valium and by the popular name “vallies”, is the world’s most popular tranquilliser. It’s very habit-forming and most people will get hooked on it if they take it for more than a couple of months. Indeed, the authorities say doctors shouldn’t prescribe it for more than four weeks. So I think it’s high time you had a talk with your GP about getting yourself off these pills. As for your daughter, all I can tell you is “vallies” can be sold on the black market in Brighton for about £1 each. I reckon you should lock up your medication where no one can get at it.