Dmha/octodrine legality in europe, preferably in latvia but generally in europe would give a good picture

Such Information can be obtained from the executive body regulating drugs in your country. For the US, that's the FDA, for New Zeeland it's Medsafe. The later also notes:

Medsafe has received advice that octodrine is a medicine as it is only added to products for a therapeutic effect, despite any absence of therapeutic purpose claims for the finished product. There does not seem to be any other reason for octodrine to be added to the product other than for a therapeutic effect

This means that Medsafe regards any product with it as a medical product. They also tell about some other jurisdictions:

Australia - In October 2017 the TGA included entries for “DMBA and other aliphatic alkylamines with stimulant properties including DMHA”, into Schedule 10 of the Poisons Standard.

USA - The FDA website includes warnings regarding DMAA, DMBA, and β-Methylphenethylamine (BMPEA) in dietary supplements. None of these substances have been determined to meet its statutory definition of a dietary ingredient.

Canada - DHMA is known as “octodrine and its salts” and is listed as prohibited on the Health Canada Cosmetic Ingredient list.

World Anti-Doping Agency (WADA) - octodrine is a prohibited substance in sports competitions under class S6 of the Prohibited List.

I can't source a Latvian source due to my lack of ability to speak and read Latvian.