“He that hath received his testimony hath set to his seal that God is true.”  
John 3:33

God is true. God cannot lie:
“God forbid: yea, let God be true, but every man a liar…”  Romans 3:4
You have to believe this and insist on living with this knowledge; concerning your health, finances, relationships, authority, let God be true.
There are other voices and other testimonies; there are other witnesses, but you should believe that witness that understands the past, present and future implications of that situation; no human being on earth can have that sort of knowledge; but God does, and he has a testimony concerning everything that concerns you.
No matter how convincing that other man’s witness is, he might have left out a detail, he might have misunderstood a certain scenario and he definitely does not have the full picture, so even if he insisted that taking that drink would kill you, God, with all of the understanding of the drink, chemicals, manufacturer, etc. tells you:
“…and if they drink any deadly thing, it shall not hurt them…”  Mark 16:18
This is his testimony concerning any challenge you might be facing or would ever face:
“Ye are of God, little children, and have overcome them…”  1John 4:4
“For whatsoever is born of God overcometh the world…”  1John 5:4