From the link above..
The ‘Fraser guidelines’ specifically relate only to contraception and sexual health. They are named after one of the Lords responsible for the Gillick judgement but who went on to address the specific issue of giving contraceptive advice and treatment to those under 16 without parental consent. The House of Lords concluded that advice can be given in this situation as long as:
He/she has sufficient maturity and intelligence to understand the nature and implications of the proposed treatment
He/she cannot be persuaded to tell her parents or to allow the doctor to tell them
He/she is very likely to begin or continue having sexual intercourse with or without contraceptive treatment
His/her physical or mental health is likely to suffer unless he/she received the advice or treatment
The advice or treatment is in the young person’s best interests.
There are several elements in this... use of established medical treatment (contraception) where there is adequate evidence that the benefits (preventing underage pregnancy) out weigh the risks (blood clots, gallbladder disease, heart attack, high blood pressure, liver cancer, stroke, depression, mood changes, headaches, etc. )
Gilick: It was determined that children under 16 can consent if they have sufficient understanding and intelligence to fully understand what is involved in a proposed treatment, including its purpose, nature, likely effects and risks, chances of success and the availability of other options.
The principles of informed consent are often skirted over in medical situations where the doctors are deemed more capable of assessing risk than patients and consent in one scenario is assumed for another.. the discussions and arguements differ depending on the position of those arguing for or against.
Some of the arguments relate to not being able to assess the risks because those risks are not shared with the patient. It is the medical practitioner's responsibility to determine if the child is capable of making that decision and for ensuring informed consent. It is often influenced by the opinions of those enforcing or assessing the situation.
My reading of Gilick and Fraser is that tehy relate to underage contraception where the alternative is underage pregnancy... but in reality, it is applied in other situations with the presumption of Gillick competance without rigerous assessment and without clear communication of benefits, risks and alternatives.