'THE first time I did this, I immediately dropped to the ground and did 50 push-ups,' Jordy says. She gets up from the bed, rubbing her hip - the place where her friend Stafford has just injected some clear fluid into her with a hypodermic syringe. Stafford isn't so sure about the effect. 'The first time I took it I thought, 'it's working]' ' she says. 'But it doesn't really happen that fast. Your mind makes it work that fast.'

Whether or not the physical effects of the injections are immediate, they are certainly dramatic, with ramifications that go beyond a quick high. This is no ordinary drug and Stafford and Jordy are not ordinary women. In fact, they may no longer be completely women at all - since the 'drug' they are injecting is the male sex hormone, testosterone.

Jordy and Stafford live in a warehouse apartment in San Francisco. They are among a growing number of predominantly lesbian and bisexual women in America who are taking testosterone with no intention of turning themselves into men. The hormone is obtained either on the black market or from sympathetic gender clinics; the goal is androgyny, and the result, some claim, is the creation of an entirely new sex.

'I never felt like a girl. Now I don't feel like a man, I just feel like me. I feel the balance is finally there,' says Stafford, who has been taking testosterone on and off for two-and-a- half years and has been injecting 200ml of Enanthate, a natural testosterone, every two weeks for the past six months. She no longer has periods and has developed biceps without working out, is much stronger, has more body and facial hair, an increased sex drive, a deeper voice, a thicker waist, a larger clitoris and slimmer hips.

Her flatmate Jordy injects 100ml a week of the synthetic testosterone Cipionate: she says that in an ideal world she would like to be a 'fully functioning hermaphrodite'. She has experienced all the same changes as Stafford, as well as having increased in height and grown out of all her shoes. 'It's a major body modification,' says Stafford. 'It's like piercing your ear times a hundred.' Both are thrilled with the effects so far. 'It is addictive - especially the sexual urge. I went from wanting sex once a week to three or four times a day. I thought it was great,' says Stafford.

The increased sex drive is probably one of the most dramatic effects of taking testosterone. Another woman, Frankie, who works for a San Francisco law firm, originally began taking it as part of a combined oestrogen-testosterone pill to counteract the symptoms of an early menopause - including loss of libido, exhaustion and the beginnings of osteoporosis. Within months her bones got stronger, she had more energy than she'd ever had in her life and her sex drive went from 'nothing' to 'waking up horny every morning'. She liked the effect so much she upped her dose to 100ml of Enanthate every two weeks and switched to injecting it, which is less damaging to the liver than taking it in pill form.

Since then her voice has dropped by at least one octave and her clitoris has become much bigger. She now leads a double life as a woman by day and a man by night. 'I'm somewhere in between male and female. I have a male vibration but I also like my female body. I have options. I can wear lipstick, and male or female clothes,' she says. Previously bisexual, since taking testosterone Frankie prefers 'feminine women' and claims she now understands men a lot more. 'I'm a feminist but I can really understand and empathise with teenage boys and the crazy things they do, like drive fast and rape girls,' she says. 'I went to a Renaissance Fair recently where all the women were in costumes with cleavages showing and it was all I could do not to grab people. Whoever is attractive to you it intensifies that a hundred times.'

Stafford also finds that she now prefers 'super-feminine' women. And monogamy is out of the question. 'I'm sexually interested in too many things now,' she says. Other 'male' traits include an inability to cry easily, increased aggression and 'being a lot colder about things'. She, too, claims to understand men more: 'Now I know why they get so angry when you cut them off in traffic. Before, I thought 'Oh, what's the matter with them?' Now it's more 'You must die for what you've done]' '

Dr Barry Zevin helps run a free clinic in San Francisco which includes a facility for transsexuals. For every 100 patients who attend for hormone treatment, he estimates that about 10 are women taking testosterone to achieve varying degrees of masculinity. Many more female-to-male transsexuals, he believes, are buying testosterone on the black market.

The full long-term effects, he says, are unknown - they certainly can include raised cholesterol levels, an increased risk of heart disease and male pattern baldness. 'It's possible that there is a decreased risk of breast and uterine cancer, but since no one has ever studied this we can't be sure. It may even increase the risk,' says Dr Zevin. 'In fact, the level of uncertainty about the safety of all this is pretty big, and there are some serious medical side effects including mood swings, people becoming more aggressive, depression, anger, and underlying mental health problems surfacing. There is also a substantial risk of liver tumours with oral testosterones - although the risks are small with injectables.' In spite of his reservations Dr Zevin continues to prescribe hormones. 'There are ethical issues about whether we should be providing this stuff but, for me, the fact that we're able to reach these people and give them primary care monitoring outweighs these concerns. I would not encourage anyone to do this, but for the most part the people coming in are already getting hormones on the black market. This way we can monitor their health and make sure they get breast checks and pap smears and general preventive medicine.'

Until Stafford found out about Dr Zevin's clinic she got her testosterone from 'a doctor who had this scam running where I would come in every two weeks and pay dollars 80 ( pounds 55) a time'. Now she and Jordy pay between dollars 15 and dollars 30 each for 10 doses and have their livers and cholesterol levels regularly monitored. In fact, they are more worried about the male- pattern baldness than liver damage. Both would consider reducing their dosage if they looked in danger of suffering substantial hair loss. In the meantime they enjoy what Jordy calls 'an interesting window on both worlds'.

'There are definite rules to living in a man's world,' says Frankie, who now uses the men's lavatory cubicles when she goes to a bar. 'In a straight establishment you don't look at any other men. Absolutely not. And you don't catch anybody's glance in the mirror. Just wash your hands and get the hell out of there. You don't start a conversation, because it's either a gay come-on or a conflict. In a gay place it's okay to glance at each other or even start a conversation in the mirror, but not in the stalls or at the urinal. But women always talk, even if they don't know each other. They might say 'Can I borrow your comb?' or 'That's a pretty dress]' A guy does not go into a straight bathroom and say 'Oh I like your tie'. Men's rooms are very quiet.'

However, the most exciting discovery for Frankie was 'that high' that she thinks all men are keeping secret. 'They've got a lot more strength. They can run longer. I need about an hour's less sleep now and have so much more basic energy. Colours are brighter, things are more three-dimensional. I feel more in the world than I used to. I used to be capable of half- hour crying fits and have monthly mood swings. Now I'm much more mellow and stable and calm. And my male friends on female hormones are experiencing the opposite - crying more, getting physically weaker, having a lower sex drive.'

'It's the best of both worlds,' says Stafford. 'You get to decide consciously your sexuality and what your body's going to look like - to a degree. I feel I'm the freest person in the world. I decide how I act, who I'm going to interact with, who I'm going to have a relationship with, how the world will perceive me and where my body is going to go. I guess you get to play God a little bit.'

(Photograph omitted)