Like many of us, i was aware of the huge benefits that the new combination drug therapies have had for people with HIV in the UK. The All-Party Parliamentary Group on Aids has always counted many people living with HIV among its friends, advisers and participants at meetings. The dramatic fall in the number of deaths has been apparent; many of the people living with HIV are much healthier than they were before.

A lot of our attention is now rightly focused on trying to extend these benefits to poorer parts of the world where HIV rates are much higher. That whether you live or die with HIV is determined by the continent you live in is one of the simpler and more offensive inequalities.

Access to the drugs is not the end of the story. We may too easily assume that people with HIV are so pleased to have the drugs that they follow doctors' orders religiously. The reality is that anti-retrovirals simply do not work for some people and for others they can go wrong. There is increasing evidence that new strains of HIV are being spread which are resistant to the drugs.

Many of these problems are caused by people not taking the drugs correctly. There is even a new piece of jargon to describe it: "compliance". Failure to comply with the prescribed drugs increases resistance, causes drugs to fail and harms the health of that person and potentially public health.

Of course instead of rushing to condemn people for not "complying", we need to try to understand why this may be. I took part in a dinner meeting, organised by GlaxoSmithKline, which revealed some very interesting factors behind this new problem. All of us who attended were asked to take part in an exercise that day. We were sent a box of coloured pills (actually sweets) and a schedule of the times of day we had to take them. I had 36 different pills to take at six different times, some with food and some without. Even for one day, it was incredibly difficult to remember and to co-ordinate the "pills" with my work, meetings and eating. If I managed to get it wrong on a one-day experiment, what must it be like if one has to do this every day for the rest of one's life, whether on holiday, having a work crisis, looking after a child or any number of other distractions?

We then heard from Dr Lorraine Sherr of the Royal Free Hospital who elaborated from a psychologist's perspective. Perhaps taking the pills comes to symbolise having this hated and terrible virus. Perhaps ignoring them for one day is an attempt to feel "normal" again. We also touched on some of the social factors that work against compliance. HIV is still so stigmatised - even in the communities that have been badly affected. How do you take a large number of pills without having to explain to friends, colleagues and family why you are doing it? While many people with HIV are willing to tell close friends and family, do they really want everyone in the bar, the office or the hostel to know?

And the communities particularly affected by HIV have their own complications. African people living in the UK come forward very late for testing, often after they are already seriously ill. The chances of getting the pills to work are reduced; even more so if they have cultural or economic barriers to contend with. There have even been reports of some people only taking some of the pills, sending the remainder to relatives in Africa. Some gay men with HIV live without the grounding influence of strong social structures. We heard that, to go along with such a punishing pill regime, people need to have an investment in and ambitions for their future. Many injecting drugs users have a difficult relationship with health services and their illegal drug use is hardly compatible with other complicated drugs.

There are also severe side-effects to the drugs which are not often talked about. Nausea, diarrhoea and fatigue are all regularly experienced. The anti-retrovirals are an incredibly powerful set of drugs and cause major physical changes, including weight loss from arms, legs and face and expansion of the stomach and upper back.

Of course, no-one with HIV is complaining about the drugs which are clearly saving lives at the moment. But this meeting was a very useful and illuminating reminder that access to the medicines is not the end of the story. Improving "compliance" turns out to require many of the changes that preventing transmission requires - namely to reduce the stigma attached to HIV and to understand the whole of people's lives not just their HIV status.