Dr Michelle Langdon risked the health of an 11-month-old girl and failed to get proper consent before using homeopathic medicine, the GMC's professional conduct committee decided on Thursday.
Dr Langdon, a partner at the Brunswick Medical Centre in Camden, north London, treated the baby's stomach infection by using a "dowsing" ritual to select a remedy, the hearing had heard.
She was found guilty of serious professional misconduct and banned from practising medicine for three months.
The GMC hearing had heard that Dr Langdon told Kira Jinkinson's mother Bethan her home was built on geopathic stress lines which might be making the child ill.
She then "dowsed" for a remedy by swinging a crystal attached to a chain over a book of herbal remedies.
She prescribed phosphorus for Kira's stomach upset at the appointment in October 2000.
Ms Jinkinson later took Kira to University College Hospital where gastroenteritis was diagnosed.
The GMC ruled that Dr Langdon put Ms Jinkinson under pressure to accept homeopathic medicine and her treatment of the baby was inadequate.
Another patient, Heather Charles, was also prescribed a herbal remedy for a sore throat after the doctor dowsed for the treatment.
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Complementary therapies are often seen as bizarre before they are adopted by the medical establishment
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David Tredinnick MP
Ms Charles was given antibiotics two days later by another doctor.
A third patient, Christopher Lemonius, was also given homeopathic remedies for a sore throat.
He later went to hospital where he was diagnosed as suffering from a throat infection and an abscess.
Dr Langdon was praised by Tory MP David Tredinnick, who said he had known her for five years.
In a written testimony, he said she always put the interests of her patients first.
"Complementary therapies are often seen as bizarre before they are adopted by the medical establishment," he added.
But Professor Michael Whitehouse, chairman of the committee, told Dr Langdon her behaviour had fallen "far short of the standards expected of a registered medical practitioner".
He added the committee recommended she ensured in future that her personal beliefs did not prejudice patients' care.