Can Minoxidil Be Used For A Long Duration?

Hi sir, Myself Waseem.i am 25 year old.i did hair transplant before 1 and half year.Doctor sugessted me hair 4u 5% and adgain tablet for 1 year.so i used it for 1 year and i got best result that everyone was shocked that its my natural hair or i wear wig.one of my friend already used minioxidil when we are in college so when he asked me secret of my hair i told him that i did hair transplant and using minioxidil 5% lotion.He told me to stop that minioxidil lotion because it has dangrous side effect because he also face side effect of that oil (his beard hair become brown) and my sister is also a doctor she told me that minioxidil long term use cause blood pressure problem.They all are scared me then i stopped using it befor 6 months and now my hair become thin and my scalp is clearly visible like ot was before :( So my questions are, 1)I consult with dermatalogis they told me to start oil again so if i start it again can i get result that i got before?? 2)If i used it for longer period like 5 years then it cause any danger side effect to my heart,brain or other parts of body?? 3)Before that i used this oil for 8 months after hair transplant and during that period i did not notice any side effect like headace,itching or swelling etc.so can it be possible that it shows side effect later i means after stopping it completely??? Sir please please reply