That's a worry, you just don't know what you are being given when the source is clandestine. Similar to someone on YT who got very sick with lung infections and was suspicious of vapes he had bought.
Yes, it is only the lady at immigration, who issues the certificate, who thinks you need one for each licence......and she gets shirty if you try to tell her!
In the absence of any mention of alcohol, I expect to see the prescription medication getting the blame from all the pot heads!
Perhaps it doesn't mix well with Irn Bru.