"Would you like to drink some?" Mr Lee, not his real name, asked me. I politely declined.
He did not want us to film his face, but he was happy enough to show me how he makes his rhino horn potion. He was now offering it to me.
He used a plate, specially made for grinding horn, it even had a picture of a Rhino on the side. For 15 minutes he had rubbed a chunk of horn round and round on the plate, mixing it with a small amount of water until he was happy with the solution.
When I refused, he downed it in one. "I use it when I have a hangover, it's very good for cleaning out the body" he said. "I even give a little spoonful to my baby when it has a fever".
The use of rhino horn as a cure for anything from a headache to cancer has surged in Vietnam over the last five years. The demand is disastrous for the population of African rhinos. This year, so far, 100 have been killed for their horns - 700 last year.
A cruel statistic: one rhino is shot by poachers every 14 hours on average.
Conservation campaigners claim demand from Vietnam threatens to drive the African Rhino to extinction.
At the CITES conference in Bangkok, which begins this weekend, Vietnam will be urged to adopt a comprehensive strategy to reduce demand for illegal rhino horn, drawn up by a group from the CITES Standing Committee, chaired by Britain.
There will also be calls for Vietnam to face trade sanctions. The World Wildlife Fund, WWF, wants the President of Vietnam to make a public statement urging people to stop using Rhino horn.
Vietnam has made policy changes aimed at trying to stop the trade and claims it is dealing with the demand but evidence suggests that the laws are being ignored and barely enforced.
In a room behind a shop in the backstreets of Hanoi, the Vietnamese capital, there is a deal on the table. Buy a whole horn and the price per gram will be cheaper.
He can get more the Vietnamese trader tells us. He has taken a photo of each one he has sold.
"If you came to my house a while ago, there would always be 60 or 70 kilos of Rhino horn, right now I only have a few kilos" he says.
Selling Rhino horn is illegal, but he is not afraid of the police. "In Vietnam you can always pay a bribe" he claims, when we ask if he is afraid of being caught.
His final price - £5000 - for 100 grams.
It does not have to be that expensive, medicine is cheaper, around £30 for a large tablet. I visit a street of shops selling rhino horn pills, it is Hanoi's traditional medicine supermarket. You take it like this, the chemist tells me, just mix it with water.
Campaigners say there is one cure for poaching, stop using endangered animals in Asian medicine. Not easy in a country where stuffed tigers are decorations in a doctors surgery. Doctor Toanh Van Xuan is evangelical about the wonders of Rhino horn.
"In my experience rhino horn has proved to be excellent, it helps detox the body, cleans the blood and boosts the immune system, I've used it myself and seen my patients get better".
I ask him how he responds to those in the West who say there is no scientific evidence that Rhino horn based medicine cures patients of anything.
"Even though there hasn't been a scientific study, to prove if rhino Horn works, history proves it does".
This demand for rhino horns in Vietnam, if it continues at this rate, is threatening to wipe out the population of a majestic animal that has been on earth for around 50 million years.