How common are they?
Before the era of HAART (highly active antiretroviral therapy) in the mid 1990s, research showed 75 per cent of gay men with HIV and men with haemophilia reported loss of interest in sex; 40 per cent erectile problems and 40 per cent problems with ejaculation. One in five women with HIV said they had lost interest in sex and 60 per cent said they had difficulties becoming aroused.
Since anti-HIV drug combination therapies became available, loss of interest in sex has gone down to 20 per cent. But sexual dysfunction persist in about one in three of the 900 people questioned. Dr Catalan said this showed sexual dysfunction was not a by-product of HAART because it was there before people with HIV started taking antiretrovirals.

Why do they happen?
Sexual response requires biological and psychosocial components to function adequately. Happy sexual function depends on both your mind and your body.

Chemical imbalances or damage to the brain, nervous system, blood or genitals can be culprits. But just as important are thoughts and feelings about sex, self and partners. To people defined by a rampant sexuality in the past, loss of sex drive can seem worse than anything and compound feelings of inadequacy.

What can be done?
Psychologists or psychiatrists (many clinics now have specialist mental health clinics to which they can refer people with HIV) will assess you and decide which investigations, if any, are needed.

Dr Catalan said some men only had problems getting hard with their regular partners but had no such problems having sex with others. Anxiety is a major issue; with most people problems are both physical and psychological. Treatments include penile pumps, injections into the penis and urethral applications. But these older methods have now been superseded by new drugs called PDE5 inhibitors. These all require sexual desire and stimuli to boost erection but have different time of action, doses and interactions.

V iagra available since 1998. Vi agra is taken about an hour before required, lasts for six to eight hours but its action can be delayed by food and can have potentially dangerous interactions with other medicines.

C ialis can be taken anything between 30 minutes and 12 hours before sex and are effective for up to 36 hours, have no interactions with food or alcohol and fewer interactions with other medicines.

L evitra is taken between 25 and 60 minutes before required in small pills, but the onset of its action may be delayed by fatty foods.

Side-effects for PDE5s can include a throbbing head, headaches, flushing of the skin, dizziness, back pain, indigestion, altered vision and nasal congestion, but these aren't a problem for everyone. Nitrates (poppers) must be avoided because they can dangerously lower blood pressure. Some protease inhibitor drugs (like ritonavir), some antibiotics (like erythromycin), anti-fungals (like fluconazole) and SSRIs (like Prozac) can also react dangerously.
People on medication for high blood pressure, or with low blood pressure or angina and those with liver problems or recent strokes are strongly advised avoid this group of drugs. You should always seek expert medical advice in advance of taking these drugs and not be tempted to buy them over the internet or from dealers.