The HPDT said the period of suspension would enable Dr Twentyman to "reflect" on the matters, as well as the ethical and professional responsibilities he has as a medical practitioner.
Dr Twentyman admitted a charge of professional misconduct and 20 particulars relating to the charge, but argued through his lawyer Harry Waalkens that the breaches did not warrant professional sanction.
The tribunal found that 18 of the 20 particulars were proven, with 16 of them requiring a penalty be applied.
It was argued to the HPDT that the particulars amounted to "very serious misconduct", aggravated by the fact it happened on multiple occasions with multiple patients over a prolonged period of time -- up to seven years in some cases.
"This was not a one-off situation," the professional conduct committee, which took the case to the HPDT, said.
The committee continued: "The prescribing and dispensing of drugs known by Dr Twentyman to be potent and which could have serious consequences to a patient's health, with potential for abuse, was highly inappropriate conduct on every level on which it is viewed.
"At the time of the prescribing and dispensing, patients had the potential to be harmed significantly by Dr Twentyman's conduct and he placed his patients at risk."
The doctor displayed a "disregard or indifference to potential health issues for his patients" as a result of his prescribing such drugs, it said.
Dr Twentyman had also altered patient records after an investigation into his practices began, which raised "questions of honesty and integrity", the committee said. This was "a very serious and fundamental breach" of his professional obligations.
In blunt terms, the committee said "there can be no trust in Dr Twentyman's practice as a general practitioner or as a men's health doctor".
"He acted unprofessionally with complete disregard for all relevant ethical and professional guidelines, and contrary to his patients' best interests."
He had brought the profession into significant disrepute, it said, and the "picture one has of Dr Twentyman and his practice of medicine is very bleak".
In his defence, Dr Twentyman's lawyers argued it was a "sad case about a doctor who had made mistakes but did what he considered was appropriate and in the interest of his patients".
The doctor still maintained "substantial support" from his patients, it was argued, and "not one patient has complained" about him.
"Many of the patients [which are] the subject of the charge remain undeterred in their support of Dr Twentyman," his lawyer said.
In a "bundle of references", Dr Twentyman was said to "deeply regret" what he had done, while his peers described him as "a thorough and professional doctor" who was "reliable and highly capable".
Dr Twentyman was based at High Street Men's Clinic in central Auckland, which specialises in men's health and treats patients for conditions such as low libido, erectile dysfunction and premature ejaculation.
Dr Twentyman's breaches include:
• Prescribing human growth hormone and testosterone without establishing an adequate clinical basis.
• Failing to undertake long-term monitoring, including for serious negative effects such as overgrowth of bones, extremities, face and jaw.
• Failing to conduct adequate physical examinations.
• Failing to keep adequate notes.
• Altering patient notes.
• Prescribing ephedrine to a patient for weight loss despite the patient having hypertension (high blood pressure).
• Prescribing pseudoephedrine in bulk despite submitting to a previous Competence Inquiry that he had stopped doing so.
