THE MERE idea of psychotherapy makes many people anxious. They know there are times in our lives when we need to talk to someone, but should that person be a psychotherapist?

Since stories about the inadequacies, even dangers, of psychotherapy now abound, it is not surprising that the public is worried. Perhaps a trusted therapist will turn out to be a charlatan? Research reported last month to the British Psychological Society established that a large number of psychologists were prepared to admit anonymously that they had had sex with their clients. People may also fear that, even if not actually setting out to harm them, a therapist might exploit them: take their money, while having nothing more skilful to offer than a listening ear - a service which a sympathetic friend might be able to provide just as well and for free. Last week, an article in the British Journal of Psychiatry by an Australian psychiatrist, Professor Gavin Andrews, was seized upon by some newspapers as evidence that psychotherapy is indeed 'no better than a chat with a friend'. This is not, in fact, what Professor Andrews wrote (on the contrary, he was concerned to show that nothing can replace a well-trained psychiatrist) - but the readiness with which this familiar criticism of psychotherapy was repeated just shows how sceptical some people, especially journalists, have become.

Articles about the dangers of psychotherapy usually mention the American former psychologist Jeffrey Masson and his book Against Therapy (Fontana 1991). I wrote the preface to the UK edition of that book because I knew that Masson's work was very important. The great men of psychotherapy have abused their power, as Masson so devastatingly demonstrated, and far too many therapists continue to do so.

A therapist is invested with immense power by his clients who want him to be able to take their pain away but not change them. They want happiness without effort. Good therapists, right from the beginning, disabuse their clients of this foolish notion. They say: 'I have no magic wand or magic word. Your pain is part of you, and for you to lose your pain you must change. I can help you, but I cannot do your work for you.'

Bad therapists try never to let their clients make this discovery. They want to keep the power their client has given them. There are three main reasons why therapists do this.

Some therapists are in love with power. They want to be charismatic figures, worshipped and obeyed by their clients. They use the methods developed by evangelical religious leaders and, while their clients might not end their lives in an inferno, they do spend their lives trapped and in pain.

Some therapists are greedy. They see a client getting better as a loss of income, and so they prevent the client from moving on to the stage where therapy is no longer needed. This is easy to do. They encourage the client to investigate his past, not in terms of seeing connections between events, but in terms of blaming parents, siblings, teachers and society. This is a seam which can be mined forever. The client remains a child with a ready excuse for his bad behaviour, which is 'I can't help what I do. I had a terrible childhood.' (In contrast, the good therapist shows the client that an explanation is not an excuse. We cannot be responsible for everything that happens to us, but we are always responsible for how we interpret everything that happens to us. We are free to choose our interpretations and we are always responsible for our choice. We can say, 'I blame my parents for ruining my life,' or we can say, 'My parents certainly handicapped me, but I don't take it personally. They'd have treated any child at that point in their lives the same way. I want to get on with my life and not be tied to the past.')

The third group of therapists who abuse their power consists of those who like to think of themselves as being exceptionally empathetic, sensitive and caring. They press their clients to their bosom (often literally as well as figuratively) like an Earth Mother with a child. They cannot bear to let their clients go, much less grow up. They need their clients, not merely to give themselves a sense of purpose, but to give themselves the feeling that they actually exist. Such therapists do not always appear to be Earth Mothers. Often they are lonely men and women who are unable to sustain any close relationship except with their clients.

So if there are so many dangerous therapists, would it indeed be better to talk to a friend?

Sadly, quite a few of us find ourselves in a situation where we have no friend we can talk to. Perhaps we are very much alone, or perhaps the people we are closest to are part of our problem. However, even if we do have a good friend, the best of friends cannot do what a good therapist can do.

How often can you expect a friend to listen with undivided attention? A therapist's time and attention are matters which you and the therapist negotiate. As a good friend yourself you need to bear in mind that your friend has problems of his or her own, but your therapist has to keep his problems to himself.

Friends want you to be happy but not to change because then they would have to change their relationship with you. The good therapist encourages you to change. Friends, not understanding change, can think that certain things you say about yourself, like how much you hate your mother, mean that you always feel like this. A good therapist knows that certain feelings like hating your mother are stages you need to go through.

People who grew up in families where the showing of emotion was forbidden often believe that if they were to give way to emotion they would go out of control and the emotion would go on forever. This is why many people are frightened to go into therapy. Friends might not understand, but good therapists do, that all emotion is self-limiting. We can't go on raging, or crying, or even laughing forever. To sort out our pain and predicament we need to consider aspects of our lives for which there is no recompense or reward - the humiliations and suffering in childhood, the disappointments of our hopes, our irreparable losses. Friends can find that the pity they feel for us is too painful to bear, and so they rush to 'make it better'. We can feel ourselves to be misunderstood, or to be expected to show a cheerfulness and forgiveness which we do not feel. A good therapist stays with us and accepts our pain.

How can you find a good therapist and avoid a bad one? Only by trial and error, I'm afraid. Professional qualifications are not a barrier to abuse of power. You simply have to assess what is going on in therapy.

Does your therapist humiliate you, mystify you, constantly demonstrate his power? If so, end therapy now.

Does your therapist encourage you to go over and over all the events in your past when other people treated you badly, and discourage you whenever you show that you want to make changes in your life and leave the past behind? If so, end therapy now.

Does your therapist make you feel guilty every time you want to miss an appointment, or talk about ending therapy, or when you talk about parts of your life where he does not feature? If so, end therapy now.

Does your therapist always give you the feeling that he accepts and values every aspect of you, that when he presents an alternative interpretation of something in your life this is a suggestion, not a criticism, and that all he wants for you is for you to take control of your life and live it how you want? Then stay in therapy until you feel you want to leave.

The author is a psychologist and writer