A new regulation is now in force allowing drug abusers to possess only one methamphetamine pill or 20 milligrammes of crystal meth, or "ice", to be eligible for rehabilitation instead of prosecution.
Public Health Minister Somsak Thepsuthin said the new regulation took effect on Monday.
"If you have one meth pill you will be arrested but have the right to seek rehabilitation. There must be proof that you are a drug addict and that responsibility rests with police," Mr Somsak said.
To effectively suppress drug abuse, police needed to persuade arrested drug offenders to name their suppliers, and then take legal action against the traffickers, the minister said.
Health spokeswoman Treechada Srithada said rehabilitation was available for offenders found with only one meth pill of not more than 100mg. For crystal meth, the ceiling was 20mg.
The new ministerial regulation replaces the previous regulation, which allowed offenders holding up to five pills to opt for rehabilitation. An opinion survey found a majority disagreed with the five-pill limit.