Welcome to HCM,
Hair loss is common in males with growing age due to male hormone and treatment depends on cause you have already consulted Dermatologist
There is no major side effect of local preparation and can use safely.
Finpecia is Finasteride which can have side effects you must know like Impotency,Abnormal ejaculation, Gynecomastia
( Enlargement of breast) Testicular pain
Even though dose is very small still you should discuss with your Dermatologist.
There is small risk of even developing prostate cancer
Nizral is anti fungal may be you have dandruff or some other fungal infection
that is why given please continue to use it.