A BBC investigation has uncovered the two men staging "Botox parties" in homes and beauty salons for people desperate to banish wrinkles.
While they were once registered nurses, both have been ordered to stop practising - making it illegal for them to prescribe medicine.
The Nursing and Midwifery Council (NMC) is investigating the BBC's findings.
The appeal of Botox parties is that procedures costing upwards of Â£400 can be half the price - with the organiser often given a free treatment.
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But clients of one man, Jonathan Henk, who calls himself "Jonny Botox", have claimed they were left in severe pain.
Mr Henk, 50, describes himself as a nurse of 26 years, but was struck off by the NMC in 2012 for having sex with a mental health patient without her consent.
He is now prescribing Botox to people for Â£200 a time - something that should only be done by registered practitioners.
An undercover reporter filmed him at a Botox party at a house in Wolverhampton, where he injected three women.
Mr Henk offered to give our reporter as much Botox as required.
Wearing gloves and taking the syringe from a flask, he prepared to inject her before she told him she had changed her mind.
Diane Roberts, 52, was a patient of Mr Henk's - but she says she was left with severe headaches after being injected with a substance that did not alter her appearance.
"It felt like someone had put an axe in the middle of my head. It was horrible," she said.
"I'm concerned as to what was being injected because I thought that Botox had an instant effect."
Botulinum toxin is a prescription-only medicine meaning it is regulated by legislation.
It can only be prescribed by a doctor, dentist or nurse in a specific patient's name - and can only be used for that patient.
Once a prescription has been written, the Botox is purchased and dispensed from a pharmacy.
It is not illegal for an untrained person to inject Botox - but the Royal College of Surgeons said laws should be tightened to ensure only those with proper training administer it.
Health Education England has published two reports with guidelines on the qualifications individuals should have - but no new laws have yet been passed.
James Kearsey advertises his services via Facebook on the page Estetica Cosmetics, and also describes himself as a nurse.
But in November 2015 he was suspended by the NMC after hiding a conviction for assault from his bosses at Russells Hall Hospital, Dudley.
Mr Kearsey agreed to a consultation at his home in Stourbridge, where he told our reporter he was a nurse consultant - "the same level as a doctor" - and that he makes thousands of pounds training others.
He sterilised her forehead and prepared to inject her before she told him she felt sick and left.
When later approached by our reporter as he attended a clinic in Blackpool, Mr Kearsey said "no comment" and ran away.
Mr Henk, of Bromsgrove, admitted he knew what he was doing was wrong.
"It's actually almost like doing a brain operation without a licence, so it is actually quite a serious offence," he said.
He denied knowledge of patients having bad side effects and said it was very rare that anyone was unhappy with his work.
"It is very rare that people get bruises. You get the odd one or two.
"Everyone said they were really happy. It's quite upsetting to hear that people aren't happy.
"I am looking at stopping and I am looking for other jobs. It's just very difficult because you've got bills to pay."
Despite breaking the law by prescribing the medicine, the legislation around cosmetic procedures continues to be a grey area.
NHS medical director Sir Bruce Keogh led a review into cosmetic surgery and non-surgical beauty treatments in 2013 in the wake of the PIP breast implant scandal.
And while the government promised new rules meaning treatments would no longer be allowed to be administered by untrained workers, legislation has not yet been passed.
The NMC said it would investigate Mr Kearsey, adding: "As he is currently temporarily suspended from the register he should not be undertaking any activity that would be done by a registered nurse, including prescribing medicines."
A spokeswoman added: "In relation to Mr Henk who has been struck off the register, he should not be claiming to be a registered nurse or undertaking any activity that would require him to be on the professional register, including prescribing medicines; to do so is a criminal offence."
Mandy Luckman is a clinical negligence lawyer for Irwin Mitchell who specialises in cosmetic surgery. "The legislation around Botox is non-existent. And yet the industry is huge," she said.
"There have been many injuries reported. The government needs to take it seriously."
A spokesman for the Department of Health said: "In adopting the recommendations of the Keogh Review, we are working to improve the safety of cosmetic interventions through better training and robust qualifications for practitioners."
*Additional reporting by Rebecca Woods
You can see this story in full on BBC Inside Out West Midlands at 19:30 GMT on BBC One on Monday 7 March, or via iPlayer for seven days afterwards.
Two disgraced nurses are making thousands of pounds a week illegally prescribing Botox to patients.