The legalization of cannabis represents an opportunity to start a cannabis business in Thailand, even for foreigners. The market value of the marijuana business is around 40 billion baht, and it is expected to grow to 70 billion baht by 2024, according to the Thai Industrial Hemp Trade Association. 
Setting up a cannabis company requires incorporating a Thai Limited Company whereby a foreigner must jointly own the company with a Thai shareholder as explained here: Company Registration in Thailand. Depending on the operations of your company, authorizations may need to be needed from the Thai Food and Drug Administration (FDA) which is the key regulator when it comes to cannabis.

• To buy & sell cannabis inside Thailand, you can start right away without additional formality, at least before the publication of the new Act.

• To grow cannabis, one must register on the mobile application or on the website “Plookganja” launched by the FDA. You just need to fill in your ID number, date of birth, and reason for growing marijuana (i.e. commercial reasons). This registration is valid for 1 year. 

• To import parts from abroad, you must seek permission in accordance with the Plant Propagation Act B.E. 2518 and the Plant Quarantine Act B.E. 2507. Importing extracts, even under 0.2% of THC, violates the Narcotics Code as the exemption from being classified as a narcotic applies only to extract from cannabis cultivated in Thailand. Such imports are therefore prohibited except for medical purposes. Also, cannabis cannot be imported to produce food or cosmetics