Dr Christian Jessen, the British TV doctor who presents Embarrassing Bodies, tonight goes undercover in an alarming documentary, testing various therapies which claim to 'rid' people of homosexuality.

In the Channel 4 documentary, Undercover Doctor: Cure Me I’m Gay, openly gay Dr Jessen explores the various controversial methods being deployed in the UK and US to ’cure’ gay patients.

These include 'aversion therapy' in UK and 'gay rehab' in the US.

We see Dr Jessen given bottle of ipecac syrup to drink, to make him vomit for hours while looking at pictures of naked men and listening to tapes telling him he is ‘worthless,’ that being gay was evil and that he should want to have sex with women.

This ‘shock therapy’ used to be deployed by doctors for treating homosexuality, ‘since probably the 1920s, 30, 40s and going on well into the 1970s and 80s,’ Dr Jessen tells Mail Online.

Patients were given injections every two hours which would make them vomit and have diarrhoea.

The theory was that, afterwards, seeing images of naked men or having homosexual thoughts, would cause a physical reaction.

No patients claimed to be cured by this method.

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During ‘right brain therapy,’ Dr Jessen went undercover, posing as ‘Adrian’, a gay man who wanted to be cured.

He visited Jerry Mungadze, an ex-church pastor, who claims to be a doctor. However, as Dr Jessen found out, Mungadze has no medical qualifications beyond a minor degree in psychology.

His ‘right brain therapy,’ which costs $250, claims to spot how gay the patient actually is, and why, by getting them to colour in a drawing of a brain.

Posing as ‘Adrian,’ Dr Jessen did this, with no prior medical consultation from Mungadze, who even admitted to being colour blind.

’Adrian’ had to describe which part of the drawing he had filled in which colour.

‘He told me the parts I’d drawn in black symbolised all the abuse I’d had as a child,’ says Dr Jessen.

‘Which is odd because I had a happy childhood and a lovely relationship with my parents.’

Unbelievably, we see Mungadze tell ’Adrian’ that the thyroid gland (the gland located in your neck) and the adrenal gland (located above the kidney) are both located in the brain.

‘What a load of absolute nonsense,’ says Dr Jessen.

‘It’s damaging because people watch his videos and actually think you can retrain the brain.’

Dr Jessen also investigated ‘gay rehab.’

Dr Jessen visits John Smid, who is now openly gay, but for years was married and living in denial.

Smid used to run a rehabilitation programme for gay men before he accepted his sexuality and retired in 2007.

'As with drug or alcohol rehabilitation, the rehab attempts to completely isolate the patient from his addiction,’ explains Dr Jessen.

For $3,000 a month, Smid’s three-month Love In Action programme would ‘take the patient away from anything he deemed gay,’ such as clothes and music.

Smid then talks Dr Jessen through 'gay rehab', as if he were still conducting the course, rifling through his suitcase and discarding anything that might 'cause us to feel sensual or sexual.'

Sorting through Dr Jessen’s CDs, Smid claims that music ‘rises up the senses,’ so he should only listen to ‘Christian music.’

Smid says his Mozart CD would be identified as ‘not Christian,’ and his Adele CD would be seen as equally inappropriate, as the singer is popular within the gay community.

Smid himself now admits: 'I’ve never met a man who experienced a change from homosexual to heterosexual.'