Family/systemic therapy is a kind of psychological therapy that deals with and talks to families often as a whole, or at least takes into account the key relationships ('systems') around people.
It involves consideration of the external relationships clients have and how those may play a role in creating or maintaining health/well-being and illness/difficulties. Sometimes these external relationships are reflected in ones we make inside ourselves as well, so altering the outside ones can bring about internal beneficial changes too.
There are many school of family therapy – some examples include systemic, structural, narrative, behavioural, and intergenerational, to name but five.
However the family therapist will in all probability meet with the patient, and initially whoever they wish to bring with them to the session. It is no longer thought necessary for a family to attend all sessions all the time, since much of the work may be accomplished in thinking about relationships as well as actually having them there in the room, though obviously sometimes that helps too and can be quicker.
The basic premise is the focus on the way we construct our world through the medium of relationships – 'No Man is an Island'. How those influence and hold or allow us freedom to develop and move in life is at the core of work. As mentioned sometimes this will have effect on the internal world as well. As an example of this therapy's effectiveness it has been shown that in some forms of depression, couple therapy is more effective at resolution than drug treatments, CBT or interpersonal (individual) psychotherapy.
There aren't many potential side-effects to the therapy. However as with all psychotherapies some people exploring difficulties may become temporarily more depressed or anxious, for example, while they sort through the issues that brought them to therapy. Any competent therapist will be able to deal with this and will have safety measures in place through liaison with colleagues if appropriate – for example a psychotherapist might have a connection with a psychiatrist to ensure that if a client became severely depressed rapid access to appropriate assessment and treatment is available.
Such incidents are extremely rare. It is naturally important to ensure that your therapist is appropriately qualified, registered and keeps up to date. It is also important to feel comfortable with them – trust your instincts as it will be almost impossible to make progress if you do not feel secure in the relationship or at the very least able to discuss such feelings. In family therapy this should apply to all the members involved, but it may not always be so if for example one family member is very uncomfortable about certain matters being discussed. Again it should at least be possible to talk about those issues in the room.