Rachel's life imploded eight years ago when she was introduced to heroin as a way of dealing with some of the particularly nasty problems life was throwing at her. "Everything seemed to go away when I used it," she says. Things descended into chaos.

Her daughter Anna was then two. She never saw Rachel inject herself, but was certainly familiar with the kit a heroin user needs. Increasingly, drugs eroded Rachel's will to mother her child. "Getting heroin became the be-all and end-all of my life. If I had no heroin, I wouldn't get up to take Anna to school. I was doing nothing with her. She would just have to look after herself till I got the next fix."

Eight years on and three years into methadone treatment, Rachel sits in a bland office block in Derby and talks about her job and her home. While her second daughter Mary, two, immaculately turned out in pink coat and perky bunches, sleeps in her arms, she tells of the support she has had from Addaction, a charity established 40 years ago this week after one mother, Mollie Craven, wrote feelingly in the Guardian's women's pages about her desperate search for help for her heroin-using teenage son.

Rachel found her way to Addaction five years ago. Case workers helped her by making a treatment plan aimed at getting her to analyse her drug use and identify trigger points. They also looked for practical ways to enable her to change her way of life; in her case, this included helping to get her on to a methadone programme. But early last year, Rachel needed extra support: clashes had developed with Anna, now 10.

"She was very clingy, sleeping in my bed and always wanting to keep an eye on me in case I was using drugs. She became really aggressive, bringing up drugs to get her own way. I didn't know how to deal with it. People who didn't understand what she was going through wanted me to take a tough line with her. But I felt I wanted her to get it out of her system in a different way. I knew what the problem was, but didn't know what to do about it."

Addaction had launched Breaking the Cycle, a four-year pilot scheme to help the children of drug users in 2005 with a £1m grant from the Zurich Community Trust. Projects were launched in London, Cumbria and, fortunately for Rachel, in Derby.

The project is a response to 11 recommendations made by the Advisory Council on the Misuse of Drugs in its 2003 report Hidden Harm, issued after the council held an inquiry into the situation of British children living with parents or guardians whose drug use is badly affecting the family. The council found that only 5% of children at risk from their parents' drug habit came to the attention of care workers - yet children living in these conditions often sustain profound life-long damage.

Addaction adds its own list of chilling facts: a child is more likely to use drugs if the parents are users; Britain has more drug users aged 15 and 16 than any other European country; 6% of Britain's 11-year-olds say they have used drugs.

Wider family issues, suggests Carmel Swan, manager of the Derby project, are not always considered by care workers, whose main concern is the addict. But dealing with that problem alone may not be enough if there are children in the family. What is the user's home like? Are the children well fed? If the drug is injected, do the children watch? Where is the gear kept? A training programme to be launched next month will help make other workers in the field aware of the broader, family-based approach to support.

"Being dependent on a substance does not make you a bad parent," says Swan. "But substance misuse can bring chaos. We have to stabilise the parent, then focus on the wider family and identify where support is needed.

"Being a user, thinking where the next fix is coming from is a full-time job - so much is going on as well as running a family unit. Once a user's drug problem has been stabilised, what has been an essential part of daily life has been taken away. They have to focus on the other things that have to be done. A parent may begin noticing that the bed her child is sleeping in is not what it should be, or that her child is not going regularly to school. We work with them on that. It's a difficult process and the fear of slipping is always there."

About 30 people have been referred to Breaking the Cycle in Derby. They are screened first to see if their needs can be met. Problems can include neglect of children: some drug users will have had bad experiences of family life and when they in turn become parents they need support, particularly in dealing with the difficult behaviour of their children. Sometimes all that may be needed is advice about access to other services.

"We try to work in a person-centred way," says Jenny Crouch, the project's coordinator in Derby. "We leave change up to the individual. The key is to build a relationship with the person and the family. If they feel you don't understand, change is going to be very difficult. There is a stigma about being a drug user and an even bigger stigma about being a user and a parent. We try to get a sense of the family dynamic and the issues and problems that are flagged up. Then we prepare a care plan. It's difficult sometimes to resist the temptation to give advice and the key is to be sensitive. If you make too many suggestions and the family cannot cope, the relationship suffers. The challenge is to prevent the client becoming dependent on you."

Crouch works with parents and children, both together and separately, and sets no limits on the number of sessions. "But you can demonstrate the improvement in how the family functions and deduce from that that children are less likely to get involved in using drugs. I am convinced that the project works. But we need to develop better education and training for social workers to help them consider the needs of the wider family."

Crouch has been working with Rachel and Anna for a year. "When I first met Jenny, I explained my background and what was going on," says Rachel. "Now we meet once a week or once a fortnight, depending how things are going. Jenny comes round and sees Anna on her own for half an hour to see if there is anything she wants to talk about. In her time with me, she doesn't make me feel bad about the past. She knows ways of dealing with things but gives me options, lets me make up my own mind. She doesn't tell me that something I have done is wrong and that I should do something else instead. I don't feel she is taking over - I am still the parent making a decision.

"Things are good now. Anna and I don't have many to-dos. She sleeps in her own bed, is more relaxed and happy. And so am I - I have a good home, a good job and two lovely kids."

Rachel is now starting voluntary work with parents and hopes eventually to find a job helping mothers who are drug users. She is happy to acknowledge the help given by Breaking the Cycle. "There are people here who don't judge you and are there for you. I wish I'd found them sooner"

· Some names have been changed. www.addaction.org.uk