..

No,there is patient/doctor confidentially..

At 18 you're an adult.

No ,

A doctor can't tell your parents if you are younger either. It is called patient confidentiality.

I think what they can or can't do may be dicated by the local laws in various countries.

In most western countries there is confidentiality betweent he Doctor and patient. I don't know how universal that is internationally.

That is true. Have to add the USA there is patient confidentality and I am not sure about other places.

Yes he can,. but only if he wants to make you uber rich by losing a kazillion dollars in a law suit. Other than that, no.