Cannabis use should be limited to medical purposes only, the chief of the Department of Medical Services said on Monday.
Director-general Somsak Akksilp warned against the recreational use of cannabis, especially among young people.
For children, cannabis should only be given to treat epilepsy when regular medicines are ineffective, he said.
For other medical purposes, cannabis should be used for palliative treatment and for cancer patients who suffer from nausea and vomiting after chemotherapy and do not respond to medication, Dr Somsak said.
He warned against the use of cannabis by people under 25 years, and for recreational purposes.
"Cannabis impacts the brain and the nervous system and especially with students, whose brains and learning capability are affected," Dr Somsak said. He urged schools, parents and others to be serious about protecting young people from cannabis use.
The Department of Medical Services emphasised that cannabis should be used for medical purposes only, and under doctors' supervision, he said.
"We know the pros well, but the cons include addiction and traffic accidents involving drivers under the influence. This already happens in other countries," Dr Somsak said.
Side effects included dry throat, palpitations, insomnia and anxiety, he said.
Dr Somsak said that the department has already set up the hotline 1165 where people can seek advice on proper cannabis use.
He said more meetings are expected to discuss the pros and cons of cannabis use.
Meanwhile, Deputy Prime Minister and Public Health Minister Anutin Charnvirakul said he expects that a cannabis and hemp draft bill which passed its first reading last week would become law as quickly as possible.
He said a House committee on vetting the draft bill will consider all public concerns about improper cannabis use, especially among adolescents who are regarded as the riskiest group for recreational use.
Mr Anutin said he was thankful for public concerns over cannabis use raised by many stakeholders. The Ministry of Public Health will look into those concerns seriously, he said.
But he said wanted to make it clear that the ministry has supported cannabis use only for medical purposes and for stimulating the country's economic growth.
Mr Anutin said improper use of cannabis has nothing to do with the government's policy on cannabis.
Concerns over the recreational use of cannabis follow the plant's decriminalisation last week, with doctors citing problems surrounding a lack of proper regulations.